Molybdenum-doped cerium dioxide nano-catalyst and preparation method thereof
By introducing molybdenum atoms into ceria to form a molybdenum-doped ceria nanocatalyst, the problem of high cost and insufficient activity of noble metal catalysts in electrocatalytic preparation of hydrogen peroxide is solved, and the conductivity and reactivity of the catalyst are improved, thus achieving the realization of the catalyst. Efficient and stable hydrogen peroxide generation.
Patent Information
- Application Number
- CN202411302955.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-19
- Publication Date
- 2025-01-07
AI Technical Summary
In the prior art, the precious metal catalysts for electrocatalyzing preparation of hydrogen peroxide are costly and have low abundance, which limits their scale application. Moreover, the conductivity of ceria is low and the active oxygen adsorption site is small, making it difficult to effectively catalyze di-electron oxygen reduction. reaction.
By introducing molybdenum atoms into ceria, a molybdenum-doped ceria nanocatalyst is formed, and a molybdenum-doped ceria nanorod is prepared by hydrothermal and high-temperature calcination, which increases oxygen vacancy and conductivity, and promotes the adsorption and activation of oxygen. , thereby improving the di-electron oxygen reduction activity.
The conductivity and reaction activity of molybdenum-doped ceria nanocatalysts are improved, and the generation selectivity and reaction stability of hydrogen peroxide are enhanced, and the hydrogen peroxide selectivity is achieved of 95% and reaction stability is achieved for more than 8 hours. Reduced production costs.
Smart Images
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Abstract
Description
Technical Field
[0001] The invention relates to the technical field of nano-catalytic material preparation, in particular to a molybdenum-doped cerium dioxide nano-catalyst and a preparation method thereof. Background Art
[0002] Hydrogen peroxide is a good preservative and oxidant. It is widely used in wastewater treatment, pulp bleaching and chemical synthesis due to its excellent properties such as strong oxidizing property, green and pollution-free. At present, traditional large-scale production methods of hydrogen peroxide, such as the anthraquinone method, have the disadvantages of high cost and poor economic benefits. Therefore, it is urgent to find an economical and environmentally friendly method to produce hydrogen peroxide.
[0003] Electrocatalytic preparation of hydrogen peroxide is a green and clean production method, but most electrocatalytic oxygen reduction still relies on precious metal-based catalysts such as Au and Pd (Chin. Chem. Lett., 2023, 34: 108446-108452), which show good catalytic performance for two-electron oxygen reduction. However, the low abundance and high price of precious metal catalysts limit their practical large-scale application. Therefore, the development of a non-precious metal catalyst with high activity, high selectivity and stability for the electrocatalytic preparation of hydrogen peroxide has become an important and urgent issue.
[0004] In recent years, metal oxides have been found to be potential two-electron oxygen reduction electrocatalysts (Chinese J. Catal., 2022, 43: 1204-1215). In particular, cerium dioxide is a common transition metal oxide with large oxygen storage capacity and Ce 4+ and Ce 3+ Reversible transformation and other advantages. However, due to its low electrical conductivity, the particles are easy to agglomerate, there are fewer active sites for oxygen adsorption, and it is difficult to effectively combine with the reaction *OOH intermediate, making it difficult for the reaction route to proceed towards the two-electron path. Zhang et al. (Inorg. Chem. Commun., 2022, 141: 109531-109535) designed defective structures and heteroatom-doped nanocatalysts to improve the electrical conductivity of cerium dioxide by oxygen vacancies, thereby promoting its oxygen evolution activity. On the other hand, Yan et al. designed tunable oxygen vacancies on the surface of Co3O4, and through the strategy of precipitation from the precursor, they strongly coupled it to nitrogen-doped carbon nanotubes, making it have high catalytic activity and selectivity for the generation of hydrogen peroxide (Mater. Today Energy., 2022, 24: 100931-100938).
[0005] As a common transition metal, molybdenum has an atomic radius similar to that of cerium atoms and has a variable valence state, which can effectively increase the number of defect sites in ceria. Therefore, if single molybdenum atoms can be introduced into the ceria lattice to promote the generation of oxygen vacancies on its surface, the number of active sites for two-electron oxygen reduction in ceria will be further increased, thereby effectively improving the efficiency of two-electron oxygen reduction.
[0006] Therefore, in view of this, the existing structural deficiencies are studied and improved, and a molybdenum-doped cerium dioxide nanocatalyst and a preparation method thereof are proposed. Summary of the invention
[0007] The purpose of the present invention is to provide a molybdenum-doped cerium dioxide nanocatalyst and a preparation method thereof to solve the problems raised in the above background technology.
[0008] To achieve the above object, the present invention provides the following technical solution: a molybdenum-doped cerium dioxide nanocatalyst, the preparation steps of which are as follows:
[0009] Step S1, synthesis of a cerium dioxide precursor: taking a certain amount of cerium nitrate (Ш) hexahydrate and sodium hydroxide to prepare aqueous solutions respectively, adding the cerium nitrate (Ш) hexahydrate aqueous solution dropwise to the sodium hydroxide aqueous solution for stirring, and transferring to a hydrothermal reaction kettle for hydrothermal reaction; after the reaction is cooled to room temperature, collecting a yellow precipitate by centrifugation, and freeze-drying it to obtain a cerium dioxide precursor;
[0010] Step S2, synthesis of cerium dioxide nanorods: the cerium dioxide precursor obtained in step S1 is placed in an agate mortar for physical grinding and uniformly placed, and then placed in a ceramic crucible, and then placed in a tube furnace for high-temperature calcination, and the tube furnace is naturally cooled to room temperature to obtain cerium dioxide nanorods;
[0011] Step S3, synthesis of molybdenum-doped cerium dioxide nanocatalyst: a certain amount of cerium dioxide nanorods prepared in the above step S2 are dispersed in deionized water, an appropriate amount of ammonium molybdate is added for stirring, a yellow precipitate is collected by centrifugation, freeze-dried, and then placed in a tubular furnace for calcination. After the tubular furnace is naturally cooled to room temperature, a molybdenum-doped cerium dioxide nanocatalyst is obtained.
[0012] Furthermore, in step S1, the molar ratio of cerium nitrate (Ш) hexahydrate to sodium hydroxide is 0.008:1.
[0013] Furthermore, in step S1, the hydrothermal reaction temperature is 100°C, the reaction time is 24h, and the freeze-drying time is 40h.
[0014] Furthermore, in step S2, the calcination atmosphere of the tubular furnace is Ar, the calcination temperature is 500°C, the calcination time is 4h, the heating rate is 5°C / min, and the cooling rate is 10°C / min.
[0015] Furthermore, in step S3, the molar ratio of ammonium molybdate to cerium dioxide is (1-2):3.
[0016] Furthermore, the deionized water used to disperse the cerium dioxide nanorods is 10-20 mL, and the freeze-drying time is 40 h.
[0017] Furthermore, the calcination atmosphere in the tubular furnace is 5% H2 / 95% Ar, the calcination temperature is 350°C, the calcination time is 2h, the heating rate is 5°C / min, and the cooling rate is 10°C / min.
[0018] Furthermore, a method for preparing a molybdenum-doped cerium dioxide nanocatalyst is applied to the preparation of the molybdenum-doped cerium dioxide nanocatalyst, characterized in that a 0.1 mol / L KOH solution is used as an electrolyte, oxygen is introduced for a certain period of time to make the electrolyte in an oxygen saturated state, and the molybdenum-doped cerium dioxide nanocatalyst is used to reduce oxygen to hydrogen peroxide.
[0019] The present invention provides a molybdenum-doped cerium dioxide nanocatalyst and a preparation method thereof, which has the following beneficial effects:
[0020] 1. The catalyst of the present invention causes the lattice distortion of the ceria nanorods by molybdenum doping, thereby forming a large number of oxygen vacancies. At the same time, the current density of the molybdenum-doped ceria nanocatalyst on the ring disk is significantly increased, and the starting potential is also significantly improved, proving that the increase in oxygen vacancies improves the conductivity and reaction activity of the molybdenum-doped ceria nanocatalyst.
[0021] 2. The oxygen vacancies generated by doping in the catalyst of the present invention can promote the adsorption and activation of oxygen, which is beneficial to the generation of *OOH intermediates and effectively reduces the adsorption energy of *OOH intermediates, thereby promoting the generation of hydrogen peroxide. The number of transferred electrons is reduced from 2.6 to about 2.1, which makes the reaction proceed toward the two-electron oxygen reduction path, thereby improving the two-electron oxygen reduction activity of the molybdenum-doped cerium dioxide nanocatalyst.
[0022] 3. The molybdenum-doped cerium dioxide nanocatalyst provided by the present invention, molybdenum is incorporated into the cerium dioxide lattice by impregnation and calcination, promoting the generation of oxygen vacancies, facilitating the adsorption and activation of oxygen, and reducing the reaction energy barrier for the generation of intermediates. Therefore, the catalyst exhibits excellent two-electron oxygen reduction performance, with 95% hydrogen peroxide selectivity and reaction stability of more than 8 hours.
[0023] 4. The present invention synthesizes cerium dioxide nanorods by simple hydrothermal and high-temperature calcination; ammonium molybdate is used as a molybdenum source, which is mixed and stirred with the above-mentioned cerium dioxide nanorod dispersion, and finally subjected to secondary high-temperature calcination to obtain a molybdenum-doped cerium dioxide nanocatalyst. The molybdenum is impregnated and calcined into the cerium dioxide nanorod lattice to promote the generation of oxygen vacancies. The catalyst has excellent two-electron oxygen reduction performance.
[0024] 5. The present invention has simple process, convenient operation, low production cost and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 The X-ray diffraction patterns of Example 1, Example 2 and the comparative example of the present invention;
[0026] Figure 2 This is a transmission electron microscope image of the nanocatalyst of Example 2 of the present invention;
[0027] Figure 3 The linear sweep voltammetric performance diagrams of Example 1, Example 2 and the comparative example of the present invention;
[0028] Figure 4 The figure is a performance diagram of the number of transferred electrons of Example 1, Example 2 and the comparative example of the present invention;
[0029] Figure 5 It is a graph showing the hydrogen peroxide selectivity of Example 1, Example 2 and a comparative example of the present invention. DETAILED DESCRIPTION
[0030] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following embodiments are used to illustrate the present invention but are not intended to limit the scope of the present invention.
[0031] See also Figures 1 to 5 The present invention provides a technical solution: a molybdenum-doped cerium dioxide nanocatalyst, which is a molybdenum-doped cerium dioxide nanocatalyst. Specifically, the morphology of cerium dioxide is nanorod-like, with a length of about 60-100nm and a width of about 5-10nm. The atomic ratio of molybdenum atoms to cerium atoms in cerium dioxide is (1-2):3. Preferably, the atomic ratio of molybdenum atoms to cerium atoms in cerium dioxide is 1:3.
[0032] Preparation of Example 1
[0033] Step S1, synthesis of cerium dioxide precursor: at room temperature, first dissolve 0.76g of cerium nitrate (Ш) hexahydrate in 20mL of deionized water to prepare solution A. 8.44g of sodium hydroxide is dissolved in 15mL of deionized water to prepare solution B. Place solution A on a magnetic stirrer and stir, and evenly add solution B to solution A, mix and stir for 30min. Then transfer the mixed solution to a 100mL hydrothermal kettle and keep it warm in a hydrothermal oven at 100°C for 24h. Collect the precipitate by centrifugation, rinse it three times with deionized water and anhydrous ethanol respectively, and freeze the product in a refrigerator for 4h.
[0034] Step S2, synthesis of cerium dioxide nanorods: freeze-dry the frozen product for 40 hours, then grind the obtained product in a mortar for 10 minutes to obtain a uniform powder. Finally, put the obtained powder into a tube furnace, heat it to 500°C at a heating rate of 5°C / min under an Ar atmosphere, and keep it warm for 4 hours, then cool it to 300°C at a rate of 10°C / min, and naturally cool it to room temperature to obtain cerium dioxide nanorods.
[0035] Step S3, synthesis of molybdenum-doped cerium dioxide nanocatalyst: take 200 mg of the above-mentioned cerium dioxide nanorods and disperse them in 10 mL of deionized water, weigh 20 mg of ammonium molybdate and add them to the dispersion and stir for 8 hours, then centrifuge the above solution to collect the precipitate, and wash it twice with deionized water; collect the washed centrifugal product and freeze it in a refrigerator for 4 hours, then freeze-dry it for 40 hours, and then grind the obtained product in a mortar for 10 minutes to obtain a uniform powder; finally, put the obtained powder into a tubular furnace, and heat it to 350°C at a heating rate of 5°C / min in a 5% H2 / 95% Ar atmosphere, and keep it warm for 2 hours, cool it to 300°C at 10°C / min, and naturally cool it to room temperature to obtain a molybdenum-doped cerium dioxide nanocatalyst.
[0036] Preparation of Example 2
[0037] Step S1, synthesis of cerium dioxide precursor: at room temperature, first dissolve 0.76g of cerium nitrate (Ш) hexahydrate in 20mL of deionized water to prepare solution A. 8.44g of sodium hydroxide is dissolved in 15mL of deionized water to prepare solution B. Place solution A on a magnetic stirrer and stir, and evenly add solution B to solution A, mix and stir for 30min. Then transfer the mixed solution to a 100mL hydrothermal kettle and keep it warm in a hydrothermal oven at 100°C for 24h. Collect the precipitate by centrifugation, rinse it three times with deionized water and anhydrous ethanol respectively, and freeze the product in a refrigerator for 4h.
[0038] Step S2, synthesis of cerium dioxide nanorods: freeze-dry the frozen product for 40 hours, then grind the obtained product in a mortar for 10 minutes to obtain a uniform powder. Finally, put the obtained powder into a tube furnace, heat it to 500°C at a heating rate of 5°C / min under an Ar atmosphere, and keep it warm for 4 hours, then cool it to 300°C at a rate of 10°C / min, and naturally cool it to room temperature to obtain cerium dioxide nanorods.
[0039] Step S3, synthesis of molybdenum-doped cerium dioxide nanocatalyst: take 200 mg of the above-mentioned cerium dioxide nanorods and disperse them in 20 mL of deionized water, weigh 40 mg of ammonium molybdate and add them to the dispersion and stir for 8 hours, then centrifuge the above solution to collect the precipitate, and wash it twice with deionized water; collect the washed centrifugal product and freeze it in a refrigerator for 4 hours, then freeze-dry it for 40 hours, then grind the obtained product in a mortar for 10 minutes to obtain a uniform powder, finally, put the obtained powder into a tubular furnace, and heat it to 350°C at a heating rate of 5°C / min in a 5% H2 / 95% Ar atmosphere, and keep it warm for 2 hours, cool it to 300°C at 10°C / min, and naturally cool it to room temperature to obtain a molybdenum-doped cerium dioxide nanocatalyst.
[0040] Preparation of Comparative Examples
[0041] Step S1, synthesis of cerium dioxide precursor: at room temperature, first dissolve 0.76g of cerium nitrate (Ш) hexahydrate in 20mL of deionized water to prepare solution A. 8.44g of sodium hydroxide is dissolved in 15mL of deionized water to prepare solution B. Place solution A on a magnetic stirrer and stir, and evenly add solution B to solution A, mix and stir for 30min. Then transfer the mixed solution to a 100mL hydrothermal kettle and keep it warm in a hydrothermal oven at 100°C for 24h. Collect the precipitate by centrifugation, rinse it three times with deionized water and anhydrous ethanol respectively, and freeze the product in a refrigerator for 4h.
[0042] Step S2, synthesis of cerium dioxide nanorods: freeze-dry the frozen product for 40 hours, then grind the obtained product in a mortar for 10 minutes to obtain a uniform powder. Finally, put the obtained powder into a tube furnace, heat it to 500°C at a heating rate of 5°C / min under an Ar atmosphere, and keep it warm for 4 hours, then cool it to 300°C at a rate of 10°C / min, and naturally cool it to room temperature to obtain cerium dioxide nanorods.
[0043] See also Figure 1-5 The present invention provides a technical solution: a molybdenum-doped cerium dioxide nanocatalyst for electrocatalytic preparation of hydrogen peroxide and a preparation method thereof.
[0044] X-ray diffraction (XRD) characterization of Example 1, Example 2 and Comparative Example
[0045] The nanocatalysts of Example 1, Example 2 and the comparative example were characterized by XRD using a Bruker D8 X-ray diffractometer with a scanning range of 10-80° and a scanning rate of 8° / min. The results are shown in FIG. Figure 1 shown.
[0046] Depend on Figure 1 It can be seen that the XRD spectra of Example 1 and the comparative example correspond to the standard card of the metal oxide cerium dioxide, indicating that after molybdenum doping, Example 1 and Example 2 retain the original crystal characteristics and no metal peak appears, indicating that there are no metal molybdenum particles in Example 1 and Example 2, proving that molybdenum exists in the cerium dioxide lattice in the form of atoms.
[0047] Example 1 Transmission Electron Microscope (TEM) Characterization
[0048] Depend on Figure 2 It can be seen that the morphology of the prepared Example 1 is nanorod-like, with a length of about 60-100 nm and a width of about 5-10 nm.
[0049] Electrochemical performance test of Example 1, Example 2 and Comparative Example
[0050] 10 mg of the nanocatalysts prepared in Example 1, Example 2 and the comparative example were dissolved in a mixed solution of 20 μL 5% Nafion solution, 780 μL isopropanol and 200 μL deionized water, and ultrasonicated in an ultrasonic cleaner for 60 min. Then 5 μL was dropped on the RRDE electrode (glassy carbon outer diameter 5.61 mm, Pt ring inner diameter 6.25 mm, Pt ring outer diameter 7.92 mm), and dried at room temperature for 10 min.
[0051] A CHI 760E electrochemical workstation was used to measure the polarization curves in 0.1 mol / L KOH saturated electrolyte with a rotating disk electrode dripped with solution as the working electrode, Ag / AgCl as the reference electrode, and a platinum wire as the counter electrode. The scanning range was 0 V-1.1 V (vs. RHE) and the electrode rotation speed was 1600 rpm.
[0052] The ring current density and the hydrogen peroxide yield in alkaline medium can be calculated using the following formulas (1) and (2) respectively.
[0053]
[0054] Among them, I d is the disk current, I r is the ring current, N is the collection efficiency (N = 0.37); A geom is the area of the Pt ring.
[0055] The electrochemical test results are as follows Figures 3 to 5 shown.
[0056] When the electrolyte is 0.1mol / L KOH solution, the electrochemical performance test results are as follows: Figures 3 to 5 shown.
[0057] Further, by Figure 3 It can be seen from the linear sweep voltammetric performance diagram that the ring current density of Example 1 and Example 2 is higher than that of the comparative example from 1 mA cm -2 Increased to 2.5 mA cm -2 The onset potential increased from about 0.7 V vs. RHE to about 0.75 V vs. RHE, indicating that the catalytic activity of the molybdenum-doped ceria nanocatalyst was significantly improved.
[0058] Further, by Figure 4 It can be seen from the number of transferred electrons of the catalyst that the number of transferred electrons of Example 1 and Example 2 is reduced from 2.6 to about 2.1 relative to the comparative example, indicating that the reaction of the molybdenum-doped cerium dioxide nanocatalyst is more inclined to a two-electron reaction pathway.
[0059] Further, by Figure 5 It can be seen that in Example 1, relative to the comparative example, the selectivity of electrocatalytic preparation of hydrogen peroxide is increased from 70% to about 95%, and the selectivity of the molybdenum-doped ceria nanocatalyst is greatly improved.
[0060] The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various implementations with various modifications suitable for specific uses.
Claims
1. A molybdenum-doped cerium dioxide nanocatalyst, characterized in that: The preparation steps are as follows: Step S1, synthesis of a cerium dioxide precursor: taking a certain amount of cerium nitrate (Ш) hexahydrate and sodium hydroxide to prepare aqueous solutions respectively, adding the cerium nitrate (Ш) hexahydrate aqueous solution dropwise to the sodium hydroxide aqueous solution for stirring, and transferring to a hydrothermal reaction kettle for hydrothermal reaction; after the reaction is cooled to room temperature, collecting a yellow precipitate by centrifugation, and freeze-drying it to obtain a cerium dioxide precursor; Step S2, synthesis of cerium dioxide nanorods: the cerium dioxide precursor obtained in step S1 is placed in an agate mortar for physical grinding and uniformly placed, and then placed in a ceramic crucible, and then placed in a tube furnace for high-temperature calcination, and the tube furnace is naturally cooled to room temperature to obtain cerium dioxide nanorods; Step S3, synthesis of molybdenum-doped cerium dioxide nanocatalyst: a certain amount of cerium dioxide nanorods prepared in the above step S2 are dispersed in deionized water, an appropriate amount of ammonium molybdate is added for stirring, a yellow precipitate is collected by centrifugation, freeze-dried, and then placed in a tubular furnace for calcination. After the tubular furnace is naturally cooled to room temperature, a molybdenum-doped cerium dioxide nanocatalyst is obtained.
2. The molybdenum-doped cerium dioxide nanocatalyst according to claim 1, characterized in that: In step S1, the molar ratio of cerium nitrate (Ш) hexahydrate to sodium hydroxide is 0.008:
1.
3. The molybdenum-doped cerium dioxide nanocatalyst according to claim 1, characterized in that: In step S1, the hydrothermal reaction temperature is 100°C, the reaction time is 24h, and the freeze-drying time is 40h.
4. The molybdenum-doped cerium dioxide nanocatalyst according to claim 1, characterized in that: In step S2, the calcination atmosphere of the tubular furnace is Ar, the calcination temperature is 500°C, the calcination time is 4h, the heating rate is 5°C / min, and the cooling rate is 10°C / min.
5. The molybdenum-doped cerium dioxide nanocatalyst according to claim 1, characterized in that: In step S3, the molar ratio of ammonium molybdate to cerium dioxide is (1-2):
3.
6. The molybdenum-doped cerium dioxide nanocatalyst according to claim 5, characterized in that: The deionized water used to disperse the cerium dioxide nanorods is 10-20 mL, and the freeze-drying time is 40 h.
7. The molybdenum-doped cerium dioxide nanocatalyst according to claim 6, characterized in that: The calcination atmosphere in the tubular furnace is 5% H2 / 95% Ar, the calcination temperature is 350°C, the calcination time is 2h, the heating rate is 5°C / min, and the cooling rate is 10°C / min.
8. A method for preparing a molybdenum-doped cerium dioxide nanocatalyst, applied to the preparation of a molybdenum-doped cerium dioxide nanocatalyst according to claim 7, characterized in that: Using 0.1 mol / L KOH solution as the electrolyte, oxygen was introduced for a certain period of time to make the electrolyte saturated with oxygen, and molybdenum-doped cerium dioxide nanocatalyst was used to reduce oxygen to hydrogen peroxide.