Cerium dioxide and a method for producing the same

Abstract

The application discloses cerium dioxide and a preparation method thereof. The preparation method comprises the following steps: 1) mixing a cerium salt solution with citric acid, sodium hydroxide and urea to obtain a mixed solution; and reacting the mixed solution at 110-200 DEG C to obtain a reaction solution; 2) performing solid-liquid separation on the reaction solution, and washing and drying the solid to obtain a precursor; and 3) calcining the precursor to obtain cerium dioxide; wherein the molar ratio of the citric acid, the sodium hydroxide, the urea and the cerium salt in the cerium salt solution is 1-10:1-10:1-60:1. The cerium dioxide obtained by the preparation method is basically spherical, has a diameter of 180-200 nm and is uniform in size.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of ceria and its preparation method. BACKGROUND

[0002] Nanometer ceria is widely used in catalysis, ceramic materials, electronic devices, ultraviolet shielding, polishing and other fields. The particle size and shape of ceria have an impact on its performance and application.

[0003] Zhou Xinmu et al. studied the preparation of spherical ceria using cerium chloride as the cerium source, NH3·H2O as the precipitant, ethylene glycol as the solvent, and polyvinylpyrrolidone (PVP) as the dispersant. Zhou Xinmu et al. also studied the preparation of ultrafine ceria powder using crystalline cerium carbonate, citric acid or citric ammonium as raw materials by complex precipitation method, with a particle size of 20-40 nm.

[0004] Luan Baoping et al. studied the hydrothermal synthesis of spindle-shaped and bouquet-shaped ceria precursors at 120°C using cerium nitrate as the cerium source and sodium citrate as the morphology control agent, and obtained the final product ceria by calcination at 500°C. They also studied the preparation of micron-sized spherical ceria by using citric acid instead of sodium citrate.

[0005] CN115448354A discloses a ceria particle and a preparation method thereof, which includes the following steps: mixing a water-soluble cerium salt and a polyol to obtain a mixed solution; subjecting the mixed solution to microwave treatment in a microwave digestion instrument to obtain a precursor reaction solution; performing solid-liquid separation on the precursor reaction solution, washing and drying the obtained solid to obtain a precursor; and calcining the precursor to obtain the ceria particle. The preparation method uses a microwave digestion instrument, which is not conducive to industrialization, and it uses an organic solvent. In addition, the obtained ceria nanospheres are not uniform in size.

[0006] CN112209422A discloses a method for preparing ceria nanospheres, which includes the following steps: adding PVP and citric acid to a mixed solution of cerium nitrate and urea, stirring uniformly, and then transferring the solution into a high-pressure reaction kettle for hydrothermal reaction to obtain a ceria nanosphere precursor. The morphology of the ceria nanospheres can be controlled by adjusting the content of citric acid. Low citric acid content can prepare multi-floc ceria nanospheres, and high citric acid content can prepare smooth nanospheres. This method requires the addition of a large amount of polyvinylpyrrolidone (PVP).

[0007] CN108017082A discloses a preparation method that is beneficial to stabilizing the color and state of nanometer ceria. The preparation method includes: reacting cerium salt with alkali solution and aging, filtering, washing the filter cake with reducing acid, and then calcining to obtain nanometer ceria with a particle size of 30-50 nm.

[0008] CN1792456A discloses a method for preparing and using nano-cerium oxide catalytic materials. The method includes: a precipitation reaction between a salt solution containing cerium ions and an alkaline solution; adding a dispersing inhibitor during or after the precipitation reaction; and then filtering, washing, drying, and calcining to obtain cerium oxide catalytic materials with nanoparticle sizes. The average particle size of the obtained cerium oxide particles is 10–100 nm. Summary of the Invention

[0009] In view of this, one object of the present invention is to provide a method for preparing cerium dioxide, wherein the cerium dioxide particles obtained by this method are substantially spherical with a diameter of 180–200 nm. The obtained nano-cerium dioxide is relatively uniform in size. Furthermore, this preparation method does not require the addition of an additional dispersant and does not employ a microwave digestion apparatus, making it suitable for industrial application. Another object of the present invention is to provide cerium dioxide obtained by the above preparation method. The present invention achieves the above objects using the following technical solutions.

[0010] On one hand, the present invention provides a method for preparing cerium dioxide, comprising the following steps:

[0011] 1) Mix cerium salt solution with citric acid, sodium hydroxide and urea to obtain a mixed solution; react the mixed solution at 110-200℃ to obtain a reaction solution;

[0012] 2) Separate the reaction solution into solid and liquid phases, and wash and dry the solid to obtain the precursor;

[0013] 3) The precursor was calcined to obtain cerium dioxide;

[0014] The molar ratio of citric acid, sodium hydroxide, urea and cerium salt in the cerium salt solution is 1-10:1-10:1-60:1.

[0015] According to the preparation method of the present invention, preferably, the cerium salt in the cerium salt solution is selected from cerium chloride or cerium nitrate.

[0016] According to the preparation method of the present invention, preferably, the concentration of the cerium salt solution is 0.01 to 2 mol / L.

[0017] According to the preparation method of the present invention, preferably, in step 1), the mixture is reacted at 110-200°C for 1-30 h.

[0018] According to the preparation method of the present invention, preferably, in step 2), alkyl alcohol and water are used for washing in sequence.

[0019] According to the preparation method of the present invention, preferably, the alkyl alcohol is selected from methanol, ethanol and isopropanol.

[0020] According to the preparation method of the present invention, preferably, in step 2), the drying temperature is 70-100℃ and the drying time is 3-12h.

[0021] According to the preparation method of the present invention, preferably, in step 3), the heating rate during calcination is 1-20℃ / min.

[0022] According to the preparation method of the present invention, preferably, in step 3), the calcination temperature is 300-900℃ and the calcination time is 2-5h.

[0023] On the other hand, the present invention also provides cerium dioxide prepared according to the preparation method described above, wherein the cerium dioxide is substantially spherical with a diameter of 180-200 nm.

[0024] The cerium dioxide prepared by the method of the present invention is basically spherical with a diameter of 180-200 nm. The obtained nano-cerium dioxide is relatively uniform in size and has good dispersibility. Furthermore, the preparation method of the present invention does not require the addition of dispersants such as polyvinylpyrrolidone, does not use organic solvents as solvents, and does not use a microwave digestion apparatus, making it suitable for industrial application. Attached Figure Description

[0025] Figure 1 This is a SEM image of the nano-cerium dioxide obtained in Example 1.

[0026] Figure 2 The image shows the XRD pattern of the nano-cerium dioxide obtained in Example 1.

[0027] Figure 3 SEM image of nano-cerium dioxide obtained in Comparative Example 1. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0029] The method for preparing cerium dioxide according to the present invention includes the following steps: (1) a hydrothermal reaction step; (2) a treatment step; and (3) a calcination step. Optionally, it also includes a raw material mixing step. A detailed description follows.

[0030] <Raw material mixing steps and hydrothermal reaction steps>

[0031] In this invention, a cerium salt solution is mixed with citric acid, sodium hydroxide, and urea to obtain a mixed solution. Specifically, citric acid, sodium hydroxide, and urea can be added to the cerium salt solution and mixed to obtain a mixed solution. The mixed solution is then reacted at 110–200°C to obtain a reaction solution.

[0032] This invention, through extensive research and experimentation, has discovered that cerium dioxide nanoparticles with a generally spherical and uniform size, approximately 200 nm in diameter, can be obtained by using a specific ratio of citric acid, sodium hydroxide, urea, and cerium salt in a hydrothermal reaction, followed by post-treatment and calcination. Currently, there are no reports on the simultaneous reaction of citric acid, sodium hydroxide, urea, and cerium salt to prepare cerium dioxide with specific morphology and diameter.

[0033] In this invention, the cerium salt in the cerium salt solution can be selected from cerium chloride or cerium nitrate, or their hydrates. Preferably, the cerium salt in the cerium salt solution is cerium nitrate.

[0034] The concentration of cerium salt in the cerium salt solution is 0.01–2 mol / L, preferably 0.02–1.5 mol / L, and more preferably 0.04–1.0 mol / L. For example, it can be 0.04 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 1.0 mol / L, etc.

[0035] In this invention, citric acid can be citric acid or its hydrate. The molar ratio of citric acid to cerium salt in the cerium salt solution can be 1 to 10:1, preferably 3 to 10:1, more preferably 5 to 8:1, and even more preferably 6 to 7.5:1. For example, it can be 5.5:1, 6:1, 6.25:1, 6.5:1, 7:1, 7.5:1, 8.0:1, 8.5:1, etc.

[0036] The molar ratio of sodium hydroxide to cerium salt in the cerium salt solution can be 1 to 10:1, preferably 3 to 10:1, more preferably 5 to 8:1, and even more preferably 6 to 7.5:1. For example, it can be 5:1, 5.5:1, 6:1, 6.5:1, 7.0:1, 7.5:1, 8.0:1, 8.5:1, 9.0:1, etc.

[0037] The molar ratio of urea to cerium salt in the cerium salt solution can be 1–60:1, preferably 5–50:1, and more preferably 10–45:1. Examples include 10:1, 15:1, 18:1, 20:1, 22:1, 25:1, 26:1, 27.5:1, 28:1, and 30:1. This invention has found that without the addition of urea, the cerium dioxide with the specific particle size of this invention cannot be obtained.

[0038] In this invention, the mixture is reacted at 110–200°C to obtain a reaction solution. This is a hydrothermal reaction, which can be carried out in a reaction vessel lined with polytetrafluoroethylene (PTFE). The reaction temperature can be 110–200°C, preferably 120–180°C, and more preferably 120–150°C. The reaction time can be 1–30 hours, preferably 5–30 hours, and more preferably 12–24 hours. This facilitates industrialization.

[0039] <Processing Steps>

[0040] The reaction solution was separated into solid and liquid phases, and the solid was washed and dried to obtain the precursor.

[0041] In this invention, solid-liquid separation can be achieved through filtration or centrifugation. The solid is washed sequentially with an alkyl alcohol and water. The alkyl alcohol is selected from methanol, ethanol, and isopropanol, preferably ethanol.

[0042] Drying can be performed using vacuum drying or other methods, with no particular restrictions. The drying temperature can be 70–100℃, and the drying time can be 3–12 hours.

[0043] <Roasting Steps>

[0044] The precursor was calcined to obtain nano-cerium dioxide.

[0045] In this invention, the heating rate during calcination is 1–20 °C / min, preferably 5–18 °C / min, and more preferably 5–15 °C / min. The calcination temperature can be 300–900 °C, preferably 400–800 °C, and more preferably 400–600 °C. The calcination time can be 2–5 h, preferably 3–5 h, and more preferably 3–4 h.

[0046] The cerium dioxide prepared by the method described in this invention is nano-cerium dioxide. The cerium dioxide particles are basically spherical, with a diameter of 180-200 nm. They are relatively uniform in size and have good dispersibility.

[0047] The test methods for the following embodiments and comparative examples are described below:

[0048] SEM: Tests were performed using a ZEISS Sigma 500 field emission scanning electron microscope.

[0049] XRD: Tests were performed using an X'Pert PRO X-ray diffractometer.

[0050] Example 1

[0051] Cerium nitrate was dissolved in water to prepare a 0.08 M cerium salt solution. Citric acid monohydrate, sodium hydroxide, and urea were added to the cerium salt solution to obtain a mixture. The mixture was placed in a reaction vessel with a polytetrafluoroethylene liner and reacted at 120°C for 24 hours, then naturally cooled to room temperature to obtain a reaction solution. The molar ratio of citric acid monohydrate, sodium hydroxide, urea, and cerium salt was 6.25:6.0:20:1.

[0052] Centrifuge the resulting reaction solution for 10 minutes, discard the supernatant, wash and dry the resulting solid to obtain the precursor.

[0053] The precursor was calcined at 400℃ for 4 hours to obtain nano-cerium dioxide.

[0054] The SEM image of the nano-cerium dioxide obtained in this embodiment is shown below. Figure 1 XRD pattern can be found Figure 2 .like Figure 1 As shown, the cerium dioxide particles are basically spherical, with a diameter of approximately 200 nm. They are relatively uniform in size. Figure 2 As shown, there are no impurity peaks in the XRD pattern, and all the test peaks are standard cerium oxide peaks, indicating that the purity of the nano-cerium dioxide formed by this method is relatively high.

[0055] Example 2

[0056] Cerium nitrate was dissolved in water to prepare a 0.08 M cerium salt solution. Citric acid monohydrate, sodium hydroxide, and urea were added to the cerium salt solution to obtain a mixture. The mixture was placed in a reaction vessel with a polytetrafluoroethylene liner and reacted at 120°C for 24 hours, then naturally cooled to room temperature to obtain the reaction solution. The molar ratio of citric acid monohydrate, sodium hydroxide, urea, and cerium salt was 6.25:6.0:27.5:1.

[0057] Centrifuge the resulting reaction solution for 10 minutes, discard the supernatant, wash and dry the resulting solid to obtain the precursor.

[0058] The precursor was calcined at 400℃ for 4 hours to obtain nano-cerium dioxide.

[0059] The cerium dioxide particles obtained in this embodiment are basically spherical, with a diameter of approximately 200 nm. They are relatively uniform in size.

[0060] Comparative Example 1

[0061] Cerium nitrate was dissolved in water to prepare a 0.08 M cerium salt solution. Citric acid monohydrate and sodium hydroxide were added to the cerium salt solution to obtain a mixture. The mixture was placed in a reaction vessel with a polytetrafluoroethylene liner and reacted at 120°C for 24 hours, then naturally cooled to room temperature to obtain a reaction solution. The molar ratio of citric acid monohydrate, sodium hydroxide, and cerium salt was 6.25:6.0:1.

[0062] Centrifuge the resulting reaction solution for 10 minutes, discard the supernatant, wash and dry the resulting solid to obtain the precursor.

[0063] The precursor was calcined at 400℃ for 4 hours to obtain nano-cerium dioxide.

[0064] The SEM image of cerium dioxide obtained in this comparative example is shown below. Figure 3 .like Figure 3As shown, the cerium dioxide particles are basically spherical, but their diameter is small, about 30 nm.

[0065] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for preparing cerium dioxide, characterized in that, Includes the following steps: 1) Add citric acid, sodium hydroxide, and urea to a cerium salt solution and mix them to obtain a mixed solution; react the mixed solution at 120-150℃ for 24-30 hours to obtain a reaction solution; 2) Separate the reaction solution into solid and liquid phases, and wash and dry the solid to obtain the precursor; 3) The precursor was calcined to obtain cerium dioxide; The molar ratio of citric acid, sodium hydroxide, urea and cerium salt in the cerium salt solution is 6-8:5-8:18-28:1; Wherein, the cerium salt in the cerium salt solution is selected from cerium chloride or cerium nitrate; the concentration of the cerium salt solution is 0.06–0.09 mol / L; The obtained cerium dioxide is basically spherical with a diameter of 180-200 nm.

2. The preparation method according to claim 1, characterized in that, In step 2), alkyl alcohol and water are used for washing in sequence.

3. The preparation method according to claim 2, characterized in that, The alkyl alcohol is selected from methanol, ethanol and isopropanol.

4. The preparation method according to claim 1, characterized in that, In step 2), the drying temperature is 70-100℃ and the drying time is 3-12h.

5. The preparation method according to claim 1, characterized in that, In step 3), the heating rate during roasting is 1 to 20 °C / min.

6. The preparation method according to claim 1, characterized in that, In step 3), the roasting temperature is 300-900℃ and the roasting time is 2-5h.

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