Preparation method of high-performance catalytic ceria

Abstract

This invention discloses a method for preparing high-performance catalytic cerium oxide, belonging to the field of rare earth cerium oxide preparation technology. The cerium oxide is prepared by the following method: (1) adding surfactant and anhydrous ethanol to a cerium salt solution, mixing, adding alkali solution, heating and stirring, cooling to obtain a slurry; (2) adding alkali solution dropwise to the slurry to adjust the pH to 9-10, heating and stirring, filtering, washing with water, and drying to obtain a precursor; (3) calcining the precursor to obtain high-performance catalytic cerium oxide. The cerium oxide prepared by this invention has a high initial specific surface area and can still maintain a high specific surface area after high-temperature aging, exhibiting excellent thermal stability and anti-sintering ability; and the particle size distribution is concentrated.

Description

Technical Field

[0001] This invention relates to the field of rare earth cerium oxide preparation technology, and specifically to a high-performance catalytic cerium oxide preparation method. Background Technology

[0002] Cerium oxide, as an important active component of three-way catalysts, plays a crucial role in the purification of motor vehicle exhaust. It can remove cerium oxide through... 4+ / Ce 3+ The reversible redox cycle effectively promotes the reduction of CO, HC compounds, and NO in exhaust gas. x The catalytic activity of CeO2 is typically positively correlated with its specific surface area. A high specific surface area in CeO2 provides more exposed active sites, thereby increasing oxygen vacancy concentration and oxygen migration capacity, which is the most direct and effective way to improve catalytic performance. However, in practical applications, especially in high-temperature environments such as vehicle exhaust purification, cerium oxide faces severe challenges in terms of thermal stability. Due to its high surface energy, cerium oxide is prone to recrystallization and grain growth under sustained high temperatures, leading to sintering. This sintering causes a sharp decrease in the specific surface area of ​​cerium oxide, and the collapse of its previously abundant microporous or mesoporous structure, significantly reducing the active sites exposed on the surface and directly resulting in a decline in catalytic efficiency. Currently, a common solution is to dope the CeO2 lattice with Zr ions to form a cerium-zirconium solid solution to inhibit grain growth and improve the material's thermal stability and oxygen storage / release capacity. In addition, methods such as doping with other rare earth or transition metal elements and constructing nanocomposite structures are used to further enhance the high-temperature anti-sintering performance and long-term catalytic activity of catalytic cerium oxide.

[0003] Chinese invention patent CN103466680A discloses a method for synthesizing cerium oxide using an anionic polyelectrolyte template. This method employs a liquid-phase precipitation process, using a soluble salt as the source and an anionic polyelectrolyte as the template agent. A precipitant is added to initiate a chemical reaction that generates cage-like precursor cerium carbonate particles. These cages are formed by spindle-shaped packing. Calcination at 400-1000℃ yields the cage-like, spindle-shaped cerium carbonate product. The resulting product has a uniform particle size distribution and a high D... 50 The surface area is 6-8 μm. After calcination at 400℃, the specific surface area reaches 80-100 m². 2 / g, after calcination at 1000℃, the specific surface area reaches 14-20m². 2 / g, the average particle size of the spindle-shaped monomers is 1-3μm. The oxide particles prepared by this method play an important role in reactions such as solid oxide fuel cells, automobile exhaust purification, and complete CO oxidation; however, their specific surface area and high-temperature stability still need to be improved. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a high-performance catalytic method for preparing cerium oxide.

[0005] A method for preparing high-performance catalytic cerium oxide includes the following steps: (1) Add surfactant and anhydrous ethanol to cerium salt solution, mix well, add alkali solution, heat and stir, cool to obtain slurry; (2) Add alkaline solution to the slurry to adjust the pH to 9-10, heat and stir, filter, wash with water and dry to obtain the precursor; (3) The precursor is calcined to obtain high-performance catalytic cerium oxide; The structural formula of the surfactant is as follows: .

[0006] In step (1), the cerium salt is one of cerium ammonium nitrate, cerium nitrate, and cerium sulfate.

[0007] In step (1), the concentration of the cerium salt solution is 0.1-0.5 mol / L.

[0008] In step (1), the molar ratio of the cerium salt, surfactant and alkali is 10:(0.05-0.1):(3-5).

[0009] In step (1), the alkaline solution is an ammonium bicarbonate solution.

[0010] In step (1), the temperature of the heating and stirring is 40-60℃ and the time is 3-5h.

[0011] In step (2), the alkaline solution is an ammonium bicarbonate solution with a concentration of 15-20 wt%.

[0012] In step (2), the temperature for heating and stirring is 60-80℃ and the time is 5-8h.

[0013] In step (3), the heating rate during calcination is 1-3℃ / min, the calcination temperature is 400-650℃, and the time is 2-6h.

[0014] The surfactant is prepared by the following method: S1: The reaction of 1,2-epoxy-4-vinylcyclohexane with hexadecyldimethyl tertiary amine yields a quaternary ammonium salt compound. The reaction equation is shown below:

[0015] S2: The reaction of a quaternary ammonium salt compound with bis(trimethylsiloxymethylsilane) yields a surfactant. The reaction equation is shown below:

[0016] Due to the adoption of the above technical solutions, the beneficial effects of the present invention include: The cerium oxide prepared by this invention has a high initial specific surface area and can maintain a high specific surface area even after high-temperature aging, exhibiting excellent thermal stability and anti-sintering ability; and the particle size distribution is concentrated. Attached Figure Description

[0017] Figure 1 This is a high-resolution mass spectrum of the surfactant prepared in Example 1.

[0018] Figure 2 Fourier transform infrared spectra of the quaternary ammonium salt compound and surfactant prepared in Example 1.

[0019] Figure 3 The image shows the X-ray diffraction pattern of cerium oxide prepared in Example 3.

[0020] Figure 4 The image shown is a scanning electron microscope (SEM) image of cerium oxide prepared in Example 3.

[0021] Figure 5 The particle size distribution diagram is shown for the cerium oxide prepared in Example 3.

[0022] Figure 6 The nitrogen adsorption-desorption isotherm of cerium oxide prepared in Example 3. Detailed Implementation

[0023] Example 1 Preparation of Surfactants S1: 300 ml of acetonitrile, 0.1 mol of 1,2-epoxy-4-vinylcyclohexane, and 0.11 mol of hexadecyl dimethyl tertiary amine were added to a reaction flask and stirred until well mixed. 10 ml of 5M hydrochloric acid solution was added dropwise over 20 min. The mixture was then refluxed for 15 h, cooled to room temperature, and rotary evaporated at 55 °C to constant weight. 200 ml of cold acetone was added and stirred to precipitate the precipitate. The precipitate was filtered, washed with cold acetone (2 × 50 ml), and dried under vacuum at 50 °C for 12 h to obtain the quaternary ammonium salt compound. Its 1H NMR spectrum data are as follows: 1 H NMR (400 MHz, Methanol-) d4) δ 5.86 – 5.70 (m, 1H), 5.15 – 5.04 (m, 3H), 4.28 – 4.14 (m, 1H), 3.84 – 3.73 (m, 1H), 3.60 – 3.41 (m, 2H), 3.23 (d, J = 1.5 Hz, 6H), 2.60 –2.41 (m, 1H), 2.13 – 2.03 (m, 1H), 2.01 – 1.91 (m, 2H), 1.83 – 1.54 (m, 5H), 1.49 – 1.23 (m, 26H), 0.95 – 0.83 (m, 3H); HRMS (m / z): 394.4046[M-Cl] + ; S2: Under nitrogen protection, 400 ml of anhydrous DMF (N,N-dimethylformamide), 200 mg of rhodium tris(triphenylphosphine) chloride, and 0.1 mol of quaternary ammonium salt compound were added to a reaction flask, stirred and mixed, and heated to 100 °C. 100 ml of anhydrous DMF solution containing 0.105 mol of bis(trimethylsiloxymethylsilane) was slowly added dropwise over 40 min. The reaction was allowed to proceed for 8 h, cooled to room temperature, and 5 g of activated carbon was added and stirred for 30 min. The mixture was filtered, and the filtrate was rotary evaporated at 85 °C to constant weight. 250 ml of ethyl acetate was added and stirred to precipitate the precipitate. The filtrate was filtered, washed with ethyl acetate (2 × 50 ml), and dried under vacuum at 50 °C for 10 h to obtain the surfactant. Its 1H NMR spectrum data are as follows: 1 H NMR (400 MHz, DMSO- d 6) δ 5.06 (d, J = 5.7 Hz, 1H), 4.10 (tt, J = 6.8, 5.5 Hz, 1H), 3.71 – 3.62 (m, 1H), 3.48 (t, J = 9.0 Hz, 2H), 3.21 (s, 6H), 2.04 – 1.21 (m, 37H), 0.93 – 0.85 (m, 3H), 0.71 – 0.59 (m, 2H), 0.07 (s, 18H), -0.17 (s, 3H); its high-resolution mass spectrum is shown below. Figure 1 As shown, HRMS (m / z): 616.4978 [M-Cl] + .

[0024] Figure 2 The figures show the Fourier transform infrared spectra of quaternary ammonium salt compounds and surfactants. As can be seen from the figures, quaternary ammonium salt compounds exhibit activity in the 3350-3450 cm⁻¹ range. -1A strong and broad -OH stretching vibration peak appears at 1060-1100 cm⁻¹. -1 The stretching vibration signal of secondary alcohol CO at 2924 cm⁻¹ indicates that the epoxy group has undergone ring opening; simultaneously, at 2924 cm⁻¹... -1 and 2853cm -1 The alkyl CH stretching vibration peak was observed at 3080 cm⁻¹, which is attributed to the hexadecyl long carbon chain structure; the characteristic signal of vinyl groups appeared at 3080 cm⁻¹. -1 1640cm -1 This indicates that the vinyl structure is retained after the quaternization reaction. The surfactant at 1260 cm⁻¹... -1 A strong and broad Si-CH symmetric bending vibration peak appeared at 1050-1080 cm⁻¹. -1 The region exhibits a very strong broad peak of Si-O-Si asymmetric stretching vibration, indicating that the siloxane grafting was successful.

[0025] Example 2 Preparation of high-performance catalytic cerium oxide (1) Add 0.25 mmol surfactant (prepared in Example 1) and 100 ml anhydrous ethanol to 500 ml of 0.1 mol / L cerium sulfate solution and mix well. Slowly add 7.5 ml of 2 mol / L ammonium bicarbonate solution, heat to 40 °C and stir for 5 h, cool to room temperature to obtain slurry; (2) Add 15wt% ammonium bicarbonate solution to the slurry to adjust the pH to 9, heat to 60℃ and stir for 8h, cool to room temperature, filter, wash the filter cake with deionized water (3×50ml), and vacuum dry at 80℃ for 10h to obtain the precursor; (3) The precursor was placed in a muffle furnace and heated to 400°C at a rate of 1°C / min in air atmosphere. It was calcined for 6 hours and then naturally cooled to room temperature to obtain high-performance catalytic cerium oxide.

[0026] Example 3 Preparation of high-performance catalytic cerium oxide (1) Add 1 mmol surfactant (prepared in Example 1) and 100 ml anhydrous ethanol to 500 ml of 0.3 mol / L cerium ammonium nitrate solution and mix well. Slowly add 30 ml of 2 mol / L ammonium bicarbonate solution, heat to 50 °C and stir for 4 h, cool to room temperature to obtain slurry; (2) Add 18wt% ammonium bicarbonate to the slurry to adjust the pH to 9.5, heat to 70℃ and stir for 7h, cool to room temperature, filter, wash the filter cake with deionized water (3×50ml), and vacuum dry at 80℃ for 10h to obtain the precursor; (3) The precursor is placed in a muffle furnace and heated to 550°C at a rate of 2°C / min in air atmosphere. It is calcined for 3 hours and then naturally cooled to room temperature to obtain high-performance catalytic cerium oxide.

[0027] Figure 3 The figure shows the X-ray diffraction pattern of the cerium oxide sample. As can be seen from the figure, within the scanning range of 2θ = 10°–80°, the main diffraction peaks appear at 28.6°, 33.1°, 47.5°, 56.4°, 59.2°, 69.5°, 76.8°, and 79.1°, corresponding to the (111), (200), (220), (311), (222), (400), (331), and (420) crystal planes of cubic CeO2, respectively. Among them, the (111) crystal plane diffraction peak at 2θ = 28.6° has the highest intensity and the sharpest peak shape, and is the characteristic main peak of this structure. No obvious amorphous inclusions or impurity diffraction peaks were observed.

[0028] Figure 4 This is a scanning electron microscope image of a cerium oxide sample. As can be seen from the image, the sample consists of a large number of particles, which are approximately spherical or near-spherical in shape, and the particle surfaces are relatively rough. Figure 5 The figure shows the particle size distribution of the cerium oxide sample. As can be seen from the figure, the particle size distribution of the sample is unimodal, and the particle size is relatively concentrated. There is no obvious bimodal or multimodal phenomenon, indicating that the cerium oxide particles did not agglomerate or grow abnormally during the preparation process. Figure 6 The figure shows the nitrogen adsorption-desorption isotherm of the cerium oxide sample. As can be seen from the figure, the isotherm exhibits a significant hysteresis loop in the relative pressure range of 0.45-0.85, indicating that the sample has a mesoporous structure.

[0029] Example 4 Preparation of high-performance catalytic cerium oxide (1) Add 2.5 mmol surfactant (prepared in Example 1) and 100 ml anhydrous ethanol to 500 ml of 0.5 mol / L cerium nitrate solution and mix well. Slowly add 50 ml of 2 mol / L ammonium bicarbonate solution, heat to 60 °C and stir for 3 h, cool to room temperature to obtain slurry; (2) Add 20wt% ammonium bicarbonate to the slurry to adjust the pH to 10, heat to 80℃ and stir for 5h, cool to room temperature, filter, wash the filter cake with deionized water (3×50ml), and vacuum dry at 80℃ for 10h to obtain the precursor; (3) The precursor was placed in a muffle furnace and heated to 650°C at a rate of 3°C / min in air atmosphere. It was calcined for 2 hours and then naturally cooled to room temperature to obtain high-performance catalytic cerium oxide.

[0030] Comparative Example 1 The preparation method of high-performance catalytic cerium oxide is basically the same as that in Example 3, except that the surfactant is replaced with an equal weight of hexadecyltrimethylammonium bromide.

[0031] Comparative Example 2 The preparation method of high-performance catalytic cerium oxide is basically the same as that in Example 3, except that the surfactant is replaced with an equal weight of surfactant prepared by the following method: The preparation method of the surfactant is basically the same as that in Example 1, except that 1,2-epoxy-4-vinylcyclohexane in step S1 is replaced with an equimolar amount of epoxybutene.

[0032] Comparative Example 3 The preparation method of high-performance catalytic cerium oxide is basically the same as that in Example 3, except that the surfactant is replaced with an equal weight of surfactant prepared by the following method: The preparation method of the surfactant is basically the same as that in Example 1, except that the hexadecyl dimethyl tertiary amine in step S1 is replaced with an equimolar amount of dodecyl dimethyl tertiary amine.

[0033] Comparative Example 4 The preparation method of high-performance catalytic cerium oxide is basically the same as that in Example 3, except that the surfactant is replaced with an equal weight of surfactant prepared by the following method: The preparation method of the surfactant is basically the same as that in Example 1, except that the bistrimethylsiloxymethylsilane in step S2 is replaced with an equimolar amount of 1,1,1,3,3,5,5-heptamethyltrisiloxane.

[0034] Comparative Example 5 The preparation method of high-performance catalytic cerium oxide is basically the same as that in Example 3, except that the ammonium bicarbonate solution used in step (2) is replaced with 18wt% ammonium carbonate solution to adjust the pH.

[0035] Comparative Example 6 The preparation method of high-performance catalytic cerium oxide is basically the same as that in Example 3, except that the ammonium bicarbonate solution used in step (2) is replaced with 18wt% ammonia solution to adjust the pH to 9.5.

[0036] Comparative Example 7 Preparation of high-performance catalytic cerium oxide (1) Add 1 mmol surfactant (prepared in Example 1) and 100 ml anhydrous ethanol to 500 ml of 0.3 mol / L cerium ammonium nitrate solution, mix well, add 18 wt% ammonium carbonate dropwise to adjust pH to 9.5, heat to 70 °C and stir for 7 h, cool to room temperature, filter, wash the filter cake with deionized water (3 × 50 ml), and vacuum dry at 80 °C for 10 h to obtain the precursor; (2) The precursor was placed in a muffle furnace and heated to 550°C at a rate of 2°C / min in air atmosphere. It was calcined for 3 hours and then naturally cooled to room temperature to obtain high-performance catalytic cerium oxide.

[0037] Comparative Example 8 The preparation method of high-performance catalytic cerium oxide is basically the same as that in Example 3, except that the heating rate in step (3) is increased to 8℃ / min, while other parameters remain unchanged.

[0038] Comparative Example 9 The preparation method of high-performance catalytic cerium oxide is basically the same as that in Example 3, except that the calcination temperature in step (3) is increased to 700°C, while other parameters remain unchanged.

[0039] The high-performance catalytic cerium oxide prepared in the examples and comparative examples were subjected to specific surface area testing, aging testing, and particle size distribution testing. The test results are shown in Table 1.

[0040] Specific surface area test: The high-performance catalytic cerium oxide prepared in the examples and comparative examples was degassed under vacuum at 200°C for 3 hours, and adsorption-desorption tests were performed using a JW-04 fully automatic nitrogen adsorption instrument. The specific surface area per unit mass was calculated using the BET method.

[0041] Aging test: The cerium oxide prepared in the examples and comparative examples was placed in a muffle furnace and heated to 1000°C at a rate of 5°C / min in air atmosphere. It was then calcined at a constant temperature for 1 hour and naturally cooled to room temperature. The specific surface area after aging was then tested.

[0042] Particle size distribution test: The particle size distribution (D10-D90) of the high-performance catalytic cerium oxide prepared in the examples and comparative examples was tested using a laser particle size analyzer. Before the test, 0.05 g of cerium oxide was added to 10 ml of deionized water and ultrasonically dispersed for 30 min.

[0043] Table 1 Performance Test Data

[0044] As can be seen from the data in Table 1, the cerium oxide prepared by the present invention has a high initial specific surface area and can maintain a high specific surface area after high-temperature aging, exhibiting excellent thermal stability and anti-sintering ability, and has a concentrated particle size distribution.

[0045] This invention employs a stepwise precipitation pre-nucleation and soft template synergistic control method to prepare high-performance catalytic cerium oxide. First, a small amount of alkaline solution is added to the cerium salt solution to allow cerium ions to slowly hydrolyze and generate primary crystal nuclei of relatively uniform size. As alkaline solution is continued to be added, the cerium-based precursor grows slowly on the basis of the primary crystal nuclei, avoiding explosive nucleation, particle coarsening, and disordered agglomeration caused by local supersaturation during the first precipitation. During nucleation, the quaternary ammonium center in the surfactant molecule attracts cerium-oxygen / cerium-hydroxyl complexes through electrostatic interactions. The ortho-hydroxyl groups can form hydrogen bonds or coordination interactions with cerium ions or cerium-hydroxyl species. The synergistic effect of these two factors guides the orderly deposition of cerium ions at the micelle interface, resulting in cerium oxide with a narrow particle size distribution. The "umbrella-like" large-volume rigid side chains of the hexadecyl and cyclohexane backbones and bis(trimethylsiloxy) groups at the hydrophobic ends generate steric hindrance during the self-assembly of the solution to form a micelle template, hindering the aggregation of the cerium precursor during precipitation and increasing the specific surface area of ​​cerium oxide. The low surface tension of the siloxane segments can reduce the capillary pressure at the gas-liquid interface during solvent evaporation, effectively resisting pore wall shrinkage and preventing framework collapse. During the high-temperature calcination stage, the precursor is converted into cerium oxide. The bis(trimethylsiloxy) groups in the surfactant form a cerium-silicon composite interface in situ on the surface or grain boundaries of cerium oxide, which acts as grain boundary pinning and diffusion barrier, inhibiting grain sintering and growth, and giving cerium oxide long-term thermal stability.

[0046] Comparative Example 2 used a surfactant that did not contain a cyclohexane structure, resulting in reduced space volume and rigidity at the hydrophobic end. This made the material more prone to agglomeration during aging and drying during the cerium precursor nucleation and growth stages, ultimately leading to a decrease in specific surface area. Comparative Example 4 skipped the pre-nucleation and aging stages in the preparation of cerium oxide and directly added alkaline solution for precipitation. This resulted in an excessively rapid cerium precursor nucleation rate, with the crystal nucleus formation rate exceeding the assembly and anchoring rate of the surfactant. This easily led to disordered agglomeration, further reducing the specific surface area.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing high performance catalytic ceria, characterized in that, Includes the following steps: (1) Add surfactant and anhydrous ethanol to cerium salt solution, mix well, add alkali solution, heat and stir, cool to room temperature to obtain slurry; (2) Adjust the pH of the slurry to 9-10 using alkaline solution, heat and stir, filter, wash with water and dry to obtain the precursor; (3) The precursor is calcined to obtain high-performance catalytic cerium oxide; The structural formula of the surfactant is as follows: 。 2. The method for preparing high-performance catalytic cerium oxide according to claim 1, characterized in that, In step (1), the cerium salt is one of cerium ammonium nitrate, cerium nitrate, and cerium sulfate.

3. The method for preparing high-performance catalytic cerium oxide according to claim 1, characterized in that, In step (1), the concentration of the cerium salt solution is 0.1-0.5 mol / L.

4. The method for preparing high-performance catalytic cerium oxide according to claim 1, characterized in that, In step (1), the molar ratio of the cerium salt, surfactant and alkali is 10:(0.05-0.1):(3-5).

5. The method for preparing high-performance catalytic cerium oxide according to claim 1, characterized in that, In step (1), the alkaline solution is an ammonium bicarbonate solution.

6. The method for preparing high-performance catalytic cerium oxide according to claim 1, characterized in that, In step (1), the temperature of the heating and stirring is 40-60℃ and the time is 3-5h.

7. The method for preparing high-performance catalytic cerium oxide according to claim 1, characterized in that, In step (2), the alkaline solution is an ammonium bicarbonate solution with a concentration of 15-20 wt%.

8. The method for preparing high-performance catalytic cerium oxide according to claim 1, characterized in that, In step (2), the temperature of the heating and stirring is 60-80℃ and the time is 5-8h.

9. The method for preparing high-performance catalytic cerium oxide according to claim 1, characterized in that, In step (3), the heating rate during calcination is 1-3℃ / min, the calcination temperature is 400-650℃, and the time is 2-6h.

10. The method for preparing high-performance catalytic cerium oxide according to claim 1, characterized in that, The surfactant is prepared by the following method: S1: The reaction of 1,2-epoxy-4-vinylcyclohexane with hexadecyldimethyl tertiary amine yields a quaternary ammonium salt compound. S2: A surfactant is obtained by reacting a quaternary ammonium salt compound with bis(trimethylsiloxymethylsilane).

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