Method for preparing CeO2-ZrO2-based oxygen storage material with high oxygen storage / release performance through multistage cooperative regulation and CeO2-ZrO2-based oxygen storage material
By multi-level synergistic regulation of the intracellular, surface, and interparticle structures of CeO2-ZrO2-based oxygen storage materials, and by introducing heterogeneous particles using precipitation and heterogeneous nucleation methods, the shortcomings of CeO2-ZrO2-based oxygen storage materials in terms of oxygen storage/release performance have been overcome, achieving highly efficient redox performance.
Patent Information
- Application Number
- CN202510992303.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-18
- Publication Date
- 2026-01-20
AI Technical Summary
Existing CeO2-ZrO2-based oxygen storage materials have room for improvement in terms of oxygen storage/release performance, especially in catalytic reactions under lean/rich fuel conditions, which affects the purification efficiency of TWC and cGPF.
By multi-level synergistic regulation of the structure and composition of CeO2-ZrO2-based oxygen storage materials within the cell, at the interface, and between particles, heterogeneous particles are introduced using precipitation, co-precipitation, and heterogeneous nucleation methods. Precipitation conditions and surface modification are optimized to form mismatched interfaces to promote low-temperature oxygen release.
It significantly improves the oxygen storage/release performance of CeO2-ZrO2-based oxygen storage materials, maintains a large specific surface area, and achieves efficient catalytic reactions under different combustion conditions.
Smart Images
Figure CN121361829A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of oxygen storage materials technology, and specifically relates to a cerium-zirconium composite oxygen storage material with high oxygen storage / release performance and its preparation method. Background Technology
[0002] Motor vehicle exhaust is one of the main sources of air pollutants, with hydrocarbons (HC) and nitrogen oxides (NOx) being the primary pollutants. x Carbon monoxide (CO) and particulate matter (PM) not only cause serious environmental pollution but are also carcinogenic, endangering human health. With a large number of gasoline vehicles on the road, primarily operating in cities, exhaust treatment has become a crucial aspect of air pollution control and environmental protection. TWC and cGPF are two important components of current gasoline vehicle exhaust purification aftertreatment systems. TWC is a three-way catalyst that can simultaneously remove three gaseous pollutants (HC, NO, CO, CO, and particulate matter) from gasoline vehicle exhaust under stoichiometric air-fuel ratio conditions. x It converts PM2.5 (CO) into harmless H2O, CO2, and N2. cGPF is a catalytic particulate filter for gasoline vehicles. It coats the inside of the filter channels with a catalyst and uses the highly efficient catalytic action of the catalyst to achieve low-temperature ignition of PM2.5.
[0003] To ensure the conversion efficiency of TWC, the exhaust air-fuel ratio must be maintained near the stoichiometric air-fuel ratio. However, gasoline engines burning at the stoichiometric air-fuel ratio consume the vast majority of oxygen in the exhaust gas. Therefore, the oxygen content used for PM oxidation in cGPF is generally below 0.7%, which undoubtedly affects the purification efficiency of cGPF. CeO2-ZrO2-based oxygen storage materials, due to their excellent oxygen storage and release properties, can adapt to catalytic reactions under lean / rich fuel conditions and are widely used as the main components of TWC and cGPF. However, they still face the application challenge of significantly improving their oxygen storage / release performance. Therefore, to meet increasingly stringent emission regulations, there is an urgent need to develop higher-performance cerium-zirconium materials. Summary of the Invention
[0004] The purpose of this invention is to provide a method for preparing CeO2-ZrO2-based oxygen storage materials with high oxygen storage / release performance through multi-stage synergistic preparation, and to achieve controllable adjustment of the oxygen storage / release performance of CeO2-ZrO2 oxygen storage materials while maintaining the specific surface area of CeO2-ZrO2 materials.
[0005] In this manual, the " / " in "high oxygen storage / release performance" means "and".
[0006] The CeO2-ZrO2-based oxygen storage material with high oxygen storage / release performance provided by the present invention can be a CeO2-ZrO2 material without additive doping or a CeO2-ZrO2 material doped with additives. The doping element corresponding to the additive doping can be at least one of alkaline earth metals, transition metals, Y elements, or elements with atomic numbers of 57 to 71.
[0007] The dopant element can exist in the form of doping into the CeO2-ZrO2 unit cell to form a solid solution, or it can be highly uniformly dispersed on the CeO2-ZrO2 surface as an oxide additive, or both of the above. The introduced additive can stabilize the structure of CeO2-ZrO2 and improve the oxygen storage / release performance of CZ.
[0008] The "multi-level regulation" described in this application refers to the design and regulation of the structure of CeO2-ZrO2-based oxygen storage materials at different scales, namely intracellular, surface interface (grain boundary) and interparticle, thereby improving the redox performance of CeO2-ZrO2-based oxygen storage materials.
[0009] The present invention provides a multi-level synergistic method for preparing CeO2-ZrO2-based oxygen storage materials with high oxygen storage / release performance. The main concept is as follows: based on precipitation, the atomic and ion arrangement within the unit cells of cerium-zirconium nanocrystals is controlled by optimizing precipitation conditions, such as selecting the preferred precipitant, precipitation temperature, or precursor concentration. Surface modification is used to control the composition and structure of the cerium-zirconium material's interface. The structure and composition between cerium-zirconium particles are controlled by introducing heterogeneous particles through co-precipitation and heterogeneous nucleation methods. Modulation of the interface structure and introduction of heterogeneous particles result in different grains and particle interfaces. The atoms at these interfaces typically exhibit mismatched configurations. This structural strain at mismatched interfaces weakens metal-oxygen bonds, promotes edge mismatches and the formation of interface oxygen defect sites, thereby inducing the low-temperature release of bulk oxygen species and improving the material's oxygen storage / release performance. Therefore, by designing and controlling the structure and composition within the unit cells, at the interface, and between particles of the cerium-zirconium material, and utilizing the synergistic effect of different scale controls, the oxygen storage / release performance of the cerium-zirconium oxygen storage material can be controllably adjusted while maintaining the specific surface area of the cerium-zirconium material.
[0010] The method for preparing CeO2-ZrO2-based oxygen storage materials with high oxygen storage / release performance through multi-stage synergistic preparation according to the present invention includes the following:
[0011] (1) Ce is prepared according to the requirements x Zr 1-x The chemical composition of O2 is determined by weighing the corresponding precursors according to the ratio of CeO2 to ZrO2, dissolving each precursor in deionized water and mixing them evenly to prepare a mixed precursor salt solution of a certain concentration.
[0012] (2) Ce was prepared using alkaline solution as a precipitant. x Zr 1-x O2 material is precipitated using at least one of the following methods: forward titration, reverse titration, and co-current titration. The titration method can be alkaline titration of salt solution, salt titration of alkaline solution, simultaneous titration of alkaline solution and salt solution, or a combination of the aforementioned titration methods. The pH of the system is controlled between 8.8 and 9.0 during the titration process. After the titration is completed, a suspension is obtained. The atomic ion arrangement within the unit cells of cerium-zirconium nanocrystals is controlled by optimizing the precipitation conditions, such as selecting a preferred precipitant, a preferred precipitation temperature, or a preferred precursor concentration.
[0013] (3) The suspension obtained in step (2) is aged for 2 to 24 hours. The aging process is carried out in an air atmosphere or an inert atmosphere at 60 to 100°C and normal pressure or in a high-pressure reactor at 60 to 100°C.
[0014] (4) After aging, the suspension is filtered and washed to obtain an intermediate solid, which is then proceeded to the next step; or the obtained solid is washed multiple times, slurried, and then aged as described in step (2) is repeated, and finally filtered, washed, and dried to obtain an intermediate solid.
[0015] (5) The maximum calcination temperature of the solid obtained in step (4) shall not exceed 1000℃. The calcination process may be a one-step calcination or a step-by-step calcination: One-step calcination involves calcining the solid obtained in step (4) at a target maximum temperature of 750-1000℃ for 3-5 hours to obtain the final CeO2-ZrO2 material; Step-by-step calcination involves first calcining the solid obtained in step (4) at 500-700℃ for 3-6 hours to obtain fresh CeO2-ZrO2 material, and then calcining the fresh CeO2-ZrO2 material at 750-1000℃ for 3-5 hours to obtain the final CeO2-ZrO2 material; The atmosphere in the one-step or step-by-step calcination process may be one or a combination of air, nitrogen, and reducing gas (such as H2 / N2 mixture); The Ce x Zr 1-x After high-temperature calcination, the specific surface area of the O2 material is not less than 50m². 2 / g.
[0016] (6) When preparing CeO2-ZrO2 materials doped with at least one element (i.e., performing surface additive doping modification), the dopant element can be introduced by precipitation, that is, in step (1), the additive precursor salt solution is directly reacted with Ce. x Zr 1-x The O2 precursor salt solution is mixed and then co-precipitated in step (2); or the impregnation method is used, that is, the auxiliary agent precursor salt solution is directly impregnated onto the intermediate obtained in step (4) or / and the fresh Ce obtained in step (5). x Zr 1-xThe surface of the O2 material is then subjected to further steps.
[0017] Furthermore, the concentration of the precursor salt solution in step (1) is 5wt%-15wt%;
[0018] Further, the precursor in step (1) is a nitrate, carbonate, acetate, etc., corresponding to cerium or zirconium, wherein the precursor of cerium is preferably cerium ammonium nitrate, and it is preferable to use an oxidizing agent to oxidize Ce(III) to Ce(IV). The oxidizing agent is preferably hydrogen peroxide.
[0019] Further, the alkaline solution in step (2) is at least one of the following: a solution of hydroxide corresponding to an alkali metal or alkaline earth metal, ammonia, ammonium carbonate, ammonium bicarbonate, and urea; the solution temperature is controlled at 40-80°C during the titration process in step (2).
[0020] Furthermore, the heating rate during calcination in step (5) is 5–10 °C / min.
[0021] Furthermore, surfactants can be added in steps (1) to (4) to adjust the pore structure of the material. The surfactants are added to the mixed precursor salt solution, or to the alkaline solution, or to the suspension after precipitation, or to the suspension after aging, or to the filter cake obtained by filtration of the suspension after aging. That is, the surfactants can be added at any stage before the composite material is calcined.
[0022] Preferably, the surfactant is selected from at least one of anionic surfactants, cationic surfactants, and nonionic surfactants; more preferably, it is selected from one or more of fatty acids, fatty alcohols, and fatty amines having 8 to 20 carbon atoms. The optimal amount of the surfactant added is 20 wt% to 55 wt% of the target CeO2-ZrO2-based oxygen storage material mass.
[0023] The above-described technical solution of the present invention, as a method for controlling the structure and composition between cerium-zirconium material particles, includes introducing heterogeneous particles through co-precipitation or heterogeneous nucleation. The heterogeneous particles are Ce particles with different compositions and structures than those prepared according to the above methods. x Zr 1-x O2, or at least one of Al2O3, or SiO2, perovskite, or spinel nanocrystals.
[0024] Preferably, the method of introducing heterogeneous particles by co-precipitation is that in step (1) Ce x Zr 1-x Add heterogeneous precursor particles to the O2 mixed precursor salt solution (the rest of the steps remain unchanged).
[0025] Preferably, the method for introducing heterogeneous particles via heterogeneous nucleation is to use the fresh Ce obtained in step (5). x Zr 1-x Using O2 material as the heterogeneous core, the heterogeneous core is mixed with a heterogeneous precursor salt solution corresponding to the heterogeneous particles to be introduced (e.g., if the heterogeneous particles are Al2O3, then the corresponding heterogeneous precursor salt solution is an aluminum nitrate solution) to obtain a mixed suspension. An alkali solution or complexing agent is added to the mixed suspension to precipitate the heterogeneous precursor salt ions onto the heterogeneous core. The resulting precipitate or gel is calcined at 750–1000°C to obtain the final Ce modified from the heterogeneous particles. x Zr 1-x O2 material.
[0026] In the above-mentioned heterogeneous nucleation method for introducing heterogeneous particles, it is further preferred that the alkaline solution can be one or more of ammonia, sodium hydroxide, ammonium carbonate, ammonium bicarbonate, and urea; and the complexing agent can be one or more of citric acid, ethylenediaminetetraacetic acid, and oxalic acid.
[0027] The above-described technical solution of the present invention serves as a method for regulating Ce. x Zr 1-x The O2 surface interface structure can be modified by surface modification, which includes surface additive doping modification (method as described in step (6) above), surface etching, or atmosphere treatment. The surface additive doping agent can be at least one of alkaline earth metals, transition metals, Y element, or elements with atomic numbers 57-71; the surface etching can be one of acid etching, alkaline etching, or plasma etching; the atmosphere treatment can be inert atmosphere treatment or reducing atmosphere treatment, or a combination of the two aforementioned atmosphere treatment methods. The surface modification can be Ce prepared under any of the above methods. x Zr 1-x Performed on O2.
[0028] In the above-mentioned technical solution of the present invention, the structure of CeO2-ZrO2-based oxygen storage material can be designed and regulated in a multi-level manner. For example, it can be prepared by a method of synergistic intracellular and grain boundary structure regulation, or by a method of synergistic grain boundary and interparticle structure and composition regulation, or by a method of synergistic intracellular and interparticle structure and composition regulation, or by a multi-level regulation method of synergistic intracellular, grain boundary and interparticle structure and composition regulation. This achieves the purpose of different-scale regulation to improve the redox performance of CeO2-ZrO2-based oxygen storage material.
[0029] Compared with the prior art, the present invention has the following beneficial effects:
[0030] This invention is based on Ce x Zr 1-xThis paper explores the scientific essence of the oxygen storage / release performance of O2 materials and the kinetic factors determining their performance. A multi-level synergistic strategy is proposed, involving optimizing precipitation conditions to control the atomic and ion arrangement within the unit cells of cerium-zirconium nanocrystals, modifying the surface composition and structure of the cerium-zirconium material's interface through surface modification, introducing heterogeneous particles via co-precipitation and heterogeneous nucleation methods to regulate the structure and composition between cerium-zirconium particles, and designing and controlling the structure within the unit cells, interfaces, and between particles. By utilizing the synergistic effects at different scales, the oxygen storage / release performance of cerium-zirconium oxygen storage materials can be controllably adjusted while maintaining the specific surface area of the cerium-zirconium material. The cerium-zirconium composite material prepared by this method possesses both a large specific surface area and excellent oxygen storage / release performance. Attached Figure Description
[0031] Figure 1 The X-ray powder diffraction patterns are those of the samples obtained in Example 1 and Comparative Example 1.
[0032] Figure 2 The results of (a) H2 temperature-programmed reduction and (b) oxygen storage capacity (OSC) tests of the samples obtained in Example 1 and Comparative Example 1 are compared.
[0033] Figure 3 The results of H2 temperature-programmed reduction of samples obtained in Comparative Example 2 and Example 5 are compared.
[0034] Figure 4 The X-ray powder diffraction patterns of the samples obtained in Comparative Example 2 and Example 5 are compared.
[0035] Figure 5 Comparison of high-magnification transmission electron microscopy images of the samples obtained in Comparative Example 2(a) and Example 4(bc).
[0036] Figure 6 The surface elemental composition of the samples obtained in Example 6 and Comparative Example 1.
[0037] Figure 7 The H2 temperature-programmed reduction curves of the samples obtained in Example 6 and Comparative Example 1 are compared. Detailed Implementation
[0038] The present invention will be further illustrated below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above-described invention, and these improvements and adjustments still fall within the scope of protection of the invention.
[0039] Example 1
[0040] (1) The composition of CeO2-ZrO2-Y2O3-La2O3 is fixed as 45wt%CeO2:45wt%ZrO2:5wt%Y2O3:5wt%La2O3. The precursor salts of cerium, lanthanum and yttrium are all nitrates. The precursor salt of zirconium is zirconium oxycarbonate. Zirconium oxycarbonate is dissolved in a certain amount of concentrated nitric acid. Mix the precursor solutions evenly to prepare a mixed precursor salt solution with a concentration of 5wt%.
[0041] (2) Back-titrate 1 / 3 of the aforementioned mixed precursor salt solution to a 3 mol / L ammonia solution, in which 40 wt% lauric acid has been added; simultaneously precipitate the remaining 2 / 3 of the aforementioned mixed precursor salt solution with a 3 mol / L ammonia-3 mol / L ammonium carbonate mixed solution, controlling the pH of the system at 8.8–9.0 during the titration process; mix the suspensions obtained from the two precipitation processes.
[0042] (3) The resulting suspension was aged at 180°C for 6 hours;
[0043] (4) Add 40wt% of polyethylene glycol, which is required to prepare oxygen storage material, directly to the aged suspension, stir evenly, then filter, and wash the filter cake with water, ammonia and salt solution to obtain the intermediate.
[0044] (5) The obtained intermediate was calcined in a nitrogen atmosphere at 500°C for 3 hours and then calcined in an air atmosphere at 600°C for 3 hours to obtain fresh material; using lanthanum nitrate as a precursor, 5 wt% of La2O3 was impregnated onto the aforementioned fresh material by an equal water pore volume impregnation method, dried and calcined at 1000°C for 4 hours to obtain La2O3 modified CeO2-ZrO2-Y2O3-La2O3, denoted as La2O3 / CeO2-ZrO2-Y2O3-La2O3.
[0045] Example 2
[0046] (1) The composition of CeO2-ZrO2-Y2O3-La2O3 was fixed at 45wt% CeO2:45wt% ZrO2:5wt% Y2O3:5wt% La2O3. The precursor salts for cerium, lanthanum, and yttrium were all nitrates, and the precursor salt for zirconium was zirconium oxycarbonate, which was dissolved using a certain amount of concentrated nitric acid. The precursor solutions were mixed evenly to prepare a 5wt% mixed precursor salt solution.
[0047] (2) Backdrop 1 / 3 of the aforementioned mixed precursor salt solution to a 3 mol / L ammonia solution, in which 20 wt% polyethylene glycol has been added; backdrop the remaining 2 / 3 of the aforementioned mixed precursor salt solution to a 3 mol / L ammonia-3 mol / L ammonium carbonate mixed solution; mix the suspensions obtained from the two precipitation processes.
[0048] (3) The resulting suspension was aged at 98°C for 6 hours;
[0049] (4) Add 40wt% of polyethylene glycol, which is required to prepare oxygen storage material, directly to the aged suspension, stir evenly, then filter, and wash the filter cake with water, ammonia and salt solution to obtain the intermediate.
[0050] (5) The obtained intermediate was calcined in air at 600°C for 3 hours and then calcined at 900°C to obtain fresh material; using lanthanum nitrate as a precursor, 5 wt% of La2O3 was impregnated onto the aforementioned fresh material by the equal water pore volume impregnation method, dried and calcined at 1000°C for 4 hours to obtain La2O3 modified CeO2-ZrO2-Y2O3-La2O3, denoted as La2O3 / CeO2-ZrO2-Y2O3-La2O3.
[0051] Example 3
[0052] (1) The composition of CeO2-ZrO2-Y2O3-La2O3 was fixed at 45wt% CeO2:45wt% ZrO2:5wt% Y2O3:5wt% La2O3. The precursor salts for cerium, lanthanum, and yttrium were all nitrates, and the precursor salt for zirconium was zirconium oxycarbonate, which was dissolved using a certain amount of concentrated nitric acid. All precursor solutions were mixed evenly to prepare a mixed precursor salt solution with a concentration of 5wt%.
[0053] (2) A mixed solution of ammonia and ammonium carbonate with a concentration of 3 mol / L, namely ammonia-ammonium carbonate buffer solution, was used as a precipitant. The salt solution and the precipitant alkaline solution were co-precipitated simultaneously. The pH of the system was controlled at 8.8 to 9.0 during the titration process to obtain a suspension.
[0054] (3) The resulting suspension was aged at 98°C for 6 hours;
[0055] (4) Add 40wt% lauric acid of the oxygen storage material to be prepared directly to the aged suspension, stir evenly, then filter, and wash the filter cake with water, ammonia and salt solution to obtain the intermediate.
[0056] (5) The obtained intermediate was calcined at 600℃ for 3h to obtain fresh material; using lanthanum nitrate as a precursor, 5wt% La2O3 was impregnated onto the aforementioned fresh material by the equal water pore volume impregnation method, dried and calcined at 1000℃ for 4h to obtain La2O3 modified CeO2-ZrO2-Y2O3-La2O3, denoted as La2O3 / CeO2-ZrO2-Y2O3-La2O3.
[0057] Comparative Example 1
[0058] This comparative example compares the effects of synergistic intracellular and grain boundary structure regulation on the oxygen storage / release performance of CeO2-ZrO2 with Example 1.
[0059] (1) The composition of CeO2-ZrO2-Y2O3-La2O3 was fixed at 45wt% CeO2:45wt% ZrO2:5wt% Y2O3:5wt% La2O3. The precursor salts for cerium, lanthanum, and yttrium were all nitrates, and the precursor salt for zirconium was zirconium oxycarbonate, which was dissolved using a certain amount of concentrated nitric acid. The precursor solutions were mixed evenly to prepare a 5wt% mixed precursor salt solution.
[0060] (2) A mixed solution of ammonia and ammonium carbonate with a concentration of 3 mol / L, namely ammonia-ammonium carbonate buffer solution, was used as a precipitant. The salt solution and the precipitant alkaline solution were co-precipitated simultaneously. The pH of the system was controlled at 8.8 to 9.0 during the titration process to obtain a suspension.
[0061] (3) The resulting suspension was aged at 98°C for 6 hours;
[0062] (4) Add 40wt% lauric acid, which is required to prepare oxygen storage material, directly to the aged suspension, stir evenly, then filter, and wash the filter cake with water, ammonia and salt solution to obtain the intermediate.
[0063] (5) The obtained intermediate was calcined at 600°C for 3 hours to obtain fresh material; the aforementioned fresh material was calcined at 1000°C for 4 hours to obtain the final CeO2-ZrO2-Y2O3-La2O3.
[0064] Depend on Figure 1 The XRD patterns show that the samples obtained in Example 1 and Comparative Example 1 are both Ce 0.5 Zr 0.5 The O2 phase. However, according to the enlarged image on the right, it can be seen that compared with Comparative Example 1, the characteristic peak of the sample obtained in Example 1 is significantly at a higher angle, which indicates that Zr in the sample obtained in Example 1 is in contrast to Ce. 0.5 Zr 0.5 The higher solid solubility in the O2 unit cell and the more uniform distribution of Ce and Zr indicate that the intracrystalline structure of CeO2-ZrO2 can be effectively controlled by optimizing the precipitation method, precipitant, and aging conditions.
[0065] Figure 2 This section compares the (a) H2 temperature-programmed reduction (H2-TPR) and (b) oxygen storage capacity (OSC) test results of the samples obtained in Example 1 and Comparative Example 1. H2-TPR and oxygen storage capacity testing are commonly used characterization methods for evaluating the oxygen storage / release performance of cerium-zirconium materials. Figure 2(a) The H2-TPR curves reveal that while the highest reduction peaks of the cerium-zirconium materials prepared in Example 1 and Comparative Example 1 are both around 573 °C, the cerium-zirconium material prepared in Example 1 exhibits two distinct low-temperature reduction peaks at 383 °C and 460 °C. This indicates that the cerium-zirconium material prepared in Example 1 is more easily reduced (releasing oxygen), and the oxygen species exhibit stronger mobility. Meanwhile, from... Figure 2 (b) It can be seen that, under the same test conditions, the cerium zirconium prepared by Example 1 has a higher oxygen storage capacity, which is nearly 3 times higher than that of Comparative Example 1. This indicates that by optimizing the precipitation method, precipitant and aging conditions to regulate the intracellular structure of CeO2-ZrO2 and the surface doping modification of the additive to regulate the surface and interface structure of CeO2-ZrO2, the oxygen storage / release performance of CeO2-ZrO2 can be significantly improved.
[0066] Example 4
[0067] (1) The composition of CeO2-ZrO2-Al2O3 (CZA) was fixed at 27wt% CeO2:21wt% ZrO2:50% Al2O3. The precursor for cerium was nitrate, the precursor for aluminum was boehmite, and the precursor salt for zircon was zirconium oxycarbonate, which was dissolved in a certain amount of concentrated nitric acid. The precursor solutions of cerium and zirconium were mixed evenly to prepare a mixed precursor salt solution with a concentration of 5wt%.
[0068] (2) Disperse boehmite in ammonia (3 mol / L)-ammonium carbonate (3 mol / L) buffer solution to form a suspension containing boehmite. Use the suspension as a precipitant to coprecipitate the cerium and zirconium mixed precursor salt solution with the alkaline solution. Control the pH of the system at 8.8-9.0 during the titration process to obtain a suspension.
[0069] (3) Add 40wt% lauric acid, which is required to prepare the oxygen storage material, directly to the suspension and stir until homogeneous;
[0070] (4) The resulting suspension was aged at 98°C for 6 hours;
[0071] (5) After filtering and drying the above suspension, dry it in an oven at 100°C for 24 hours to obtain a dried material intermediate;
[0072] (6) Using lanthanum nitrate as a precursor, 5 wt% of La2O3 was impregnated onto the aforementioned dry material intermediate by an equal water pore volume impregnation method. After drying and calcining at 1000℃ for 4 h, La2O3 modified CeO2-ZrO2-Al2O3 was obtained, denoted as La2O3 / CeO2-ZrO2-Al2O3.
[0073] Example 5
[0074] (1) The composition of CeO2-ZrO2-Al2O3 was fixed at 27wt% CeO2:21wt% ZrO2:50% Al2O3. The precursor salts for cerium and aluminum were both nitrates, and the precursor salt for zirconium was zirconium oxycarbonate, which was dissolved using a certain amount of concentrated nitric acid. All precursor solutions were mixed evenly to prepare a mixed precursor salt solution with a concentration of 5wt%.
[0075] (2) Backdrop 1 / 3 of the aforementioned mixed precursor salt solution to a 3 mol / L ammonia solution, in which 20 wt% polyethylene glycol has been added; backdrop the remaining 2 / 3 of the aforementioned mixed precursor salt solution to a 3 mol / L ammonia-3 mol / L ammonium carbonate mixed solution; mix the suspensions obtained from the two precipitation processes.
[0076] (3) Add 40wt% lauric acid, the oxygen storage material, directly to the suspension and stir until homogeneous;
[0077] (4) The resulting suspension was aged at 98°C for 6 hours;
[0078] (5) After filtering and drying the above suspension, calcining it in air at 600°C for 3 hours to obtain a dried material intermediate;
[0079] (6) The aforementioned intermediate was calcined at 1000°C for 4 h in a 5% H2 / N2 atmosphere to obtain CeO2-ZrO2-Al2O3.
[0080] Comparative Example 2 compares the effects of synergistic intracellular, grain boundary, and particle structure regulation on the oxygen storage / release performance of CeO2-ZrO2-Al2O3.
[0081] (1) The composition of CeO2-ZrO2-Al2O3 was fixed at 27wt% CeO2:21wt% ZrO2:50% Al2O3. The precursor salts for cerium and aluminum were both nitrates, and the precursor salt for zirconium was zirconium oxycarbonate, which was dissolved using a certain amount of concentrated nitric acid. All precursor solutions were mixed evenly to prepare a mixed precursor salt solution with a concentration of 5wt%.
[0082] (2) A mixed solution of 3 mol / L ammonia and 3 mol / L ammonium carbonate was used as a precipitant to co-precipitate the mixed precursor salt solution with the alkaline solution. The pH of the system was controlled at 8.8 to 9.0 during the titration process to obtain a suspension.
[0083] (3) Add 40wt% lauric acid, which is required to prepare the oxygen storage material, directly to the suspension and stir until homogeneous;
[0084] (4) The resulting suspension was aged at 98°C for 6 hours;
[0085] (5) After filtering and drying the above suspension, calcine it in air at 600°C for 3 hours to obtain fresh material; calcine the aforementioned fresh material at 1000°C for 4 hours to obtain CeO2-ZrO2-Al2O3.
[0086] Figure 3 This is a comparison of the H2 temperature-programmed reduction results of the samples obtained in Comparative Example 2 and Example 5. Figure 3 As shown, the sample obtained in Example 5 has a lower reduction peak and a larger reduction peak area than that in Comparative Example 2. This indicates that the former has a better oxygen release capacity. This shows that by optimizing the precipitation method, precipitant, and calcination atmosphere (calcination under H2 / N2 atmosphere promotes the crystal phase transformation of CZ, so a new phase will appear in the local area of CZ grains) to regulate the composition and structure of the intracellular and surface interfaces of CeO2-ZrO2-Al2O3 material, its oxygen release performance can be significantly improved.
[0087] Figure 4 It can be seen that although the samples obtained in Comparative Example 2 and Example 5 have similar XRD diffraction patterns, the magnified image shows that the sample obtained in Example 5 has a weaker diffraction peak at around 14°, which proves that the surface and interface structure of the sample obtained in Example 5 has changed.
[0088] Figure 5 Comparison of high-magnification transmission electron microscopy images of the samples obtained in Comparative Example 2(a) and Example 4(bc) Figure 5 Region I is assigned to the (111) crystal plane of CeO2-ZrO2, Region II to the (200) crystal plane of Al2O3, and Region III to the (110) crystal plane of LaAlO3. Compared with Comparative Example 2, characteristic crystal planes of LaAlO3 were also detected in Example 4, indicating that heterogeneous particles are indeed present in the sample obtained in Example 4.
[0089] Example 6
[0090] (1) The composition of CeO2-ZrO2-Y2O3-La2O3 was fixed at 45wt% CeO2:45wt% ZrO2:5wt% Y2O3:5wt% La2O3. The precursor salts for cerium, lanthanum, and yttrium were all nitrates, and the precursor salt for zirconium was zirconium oxycarbonate, which was dissolved using a certain amount of concentrated nitric acid. The precursor solutions were mixed evenly to prepare a 5wt% mixed precursor salt solution.
[0091] (2) A mixed solution of 3 mol / L ammonia and 3 mol / L ammonium carbonate was used as a precipitant and co-precipitated with the alkaline solution. The pH of the system was controlled at 8.8 to 9.0 during the titration process to obtain a suspension.
[0092] (3) The resulting suspension was aged at 98°C for 6 hours;
[0093] (4) Add 40wt% lauric acid, an oxygen storage material, directly to the aged suspension, stir evenly, then filter, and wash the filter cake with water, ammonia, and salt solution to obtain the intermediate.
[0094] (5) The obtained intermediate was calcined at 600℃ for 3 hours to obtain fresh material, which was used as the "heterogeneous nucleus";
[0095] (6) After combining 20g of the "heterogeneous core" with 1g of LaMnO3 corresponding to lanthanum nitrate and manganese nitrate, a certain amount of deionized water was added and stirred evenly to obtain a suspension. Then, a certain amount of citric acid was added to the obtained suspension. Based on 1g of target LaMnO3 (LaMnO3 is the introduced heterogeneous particle), the molar amount of citric acid added was the same as that of LaMnO3. 3+ and Mn 3+ The total molar ratio is 1:1.
[0096] (7) Stir the above suspension continuously in an 80°C water bath until the suspension becomes gel-like, then stop stirring.
[0097] (8) After drying the gel obtained in step (7) at 90°C for 12 hours, calcining it in air at 750°C for 3 hours will yield the target 5wt% LaMnO3 / CeO2-ZrO2-Y2O3-La2O3 composite oxygen storage material.
[0098] Comparative Example 3 and Example 6 compare the effect of introducing heterogeneous particles on the low-temperature reduction performance of CeO2-ZrO2.
[0099] The preparation method of CeO2-ZrO2-Y2O3-La2O3 oxygen storage material in Comparative Example 3 is the same as that in Comparative Example 1, except that the final calcination conditions of the obtained CeO2-ZrO2-Y2O3-La2O3 are calcination at 750°C in air atmosphere for 3 hours.
[0100] Figure 6 For the surface elemental composition analysis of the samples obtained in Example 6 and Comparative Example 1, by Figure 6 It can be seen that Mn and La are enriched on the surface of Example 6, which also confirms the successful introduction of heterogeneous particles in the method described in Example 6.
[0101] Figure 7 A comparison of the H2 temperature-programmed reduction curves of the samples obtained in Example 6 and Comparative Example 3. Figure 7The H2-TPR curves revealed that the highest reduction peak of the cerium-zirconium material prepared in Comparative Example 3 was around 576℃, while the highest reduction peak of the cerium-zirconium material prepared in Example 6 decreased to 484℃, and a significant low-temperature shoulder peak appeared around 240℃. This indicates that the cerium-zirconium material prepared in Example 6 is more easily reduced (releasing oxygen), and the oxygen species have stronger mobility. This demonstrates that introducing heterogeneous particles to regulate the structure of grain boundaries and interparticles can improve the low-temperature reduction performance of CeO2-ZrO2.
Claims
1. A CeO2-ZrO2-based oxygen storage material with high oxygen storage / release performance, characterized in that, It is a CeO2-ZrO2 material without additive doping, or a CeO2-ZrO2 material with additive doping. The doping element corresponding to the additive doping can be at least one of alkaline earth metals, transition metals, Y element, or elements with atomic numbers from 57 to 71.
2. A method for multi-stage synergistic preparation of CeO2-ZrO2-based oxygen storage materials with high oxygen storage / release performance, characterized in that, Includes the following: (1) Based on the Ce to be prepared x Zr 1-x The chemical composition of O2 is determined by weighing the corresponding precursors according to the ratio of CeO2 to ZrO2, dissolving each precursor in deionized water and mixing them evenly to prepare a mixed precursor salt solution of a certain concentration. (2) Ce was prepared using alkaline solution as a precipitant. x Zr 1-x O2 material, the precipitation method is at least one of the following: forward titration, reverse titration, and co-current titration. The titration method is to titrate a salt solution with an alkali solution, or to titrate an alkali solution with a salt solution, or to titrate both alkali and salt solutions simultaneously, or a combination of the above titration methods. The pH of the system is controlled at 8.8 to 9.0 during the titration process. After the titration is completed, a suspension is obtained. (3) The suspension obtained in step (2) is aged for 2 to 24 hours. The aging process is carried out in an air atmosphere or an inert atmosphere at 60 to 100°C and normal pressure or in a high-pressure reactor at 60 to 100°C. (4) After filtration and washing of the aged suspension, an intermediate solid is obtained and proceeded to the next step; or the obtained solid is washed repeatedly, slurried and then aged in step (2) again, and finally filtered, washed and dried to obtain an intermediate solid. (5) The solid obtained in step (4) is subjected to one-step calcination or step-by-step calcination: one-step calcination is to calcine the solid obtained in step (4) at a target maximum temperature of 750-1000℃ for 3-5 hours to obtain the final CeO2-ZrO2 material; step-by-step calcination is to first calcine the solid obtained in step (4) at 500-700℃ for 3-6 hours to obtain fresh CeO2-ZrO2 material, and then calcine the fresh CeO2-ZrO2 material at 750-1000℃ for 3-5 hours to obtain the final CeO2-ZrO2 material; the one-step or step-by-step calcination is carried out under at least one of air atmosphere, nitrogen atmosphere, and reducing gas atmosphere. (6) When preparing CeO2-ZrO2 materials doped with at least one element, a precipitation method is used, that is, in step (1), the auxiliary agent precursor salt solution is directly reacted with Ce. x Zr 1-x The O2 precursor salt solution is mixed and then co-precipitated in step (2); or the impregnation method is used, that is, the auxiliary precursor salt solution corresponding to the dopant element is directly impregnated onto the intermediate obtained in step (4) or / and the fresh Ce obtained in step (5). x Zr 1-x The surface of the O2 material is then subjected to further steps.
3. The method according to claim 2, characterized in that, In step (1), the mass concentration of the precursor salt solution is 5% to 15%.
4. The method according to claim 2, characterized in that, The precursor in step (1) is at least one of the nitrate, carbonate and acetate of cerium and zirconium, wherein the precursor of cerium is cerium ammonium nitrate, and is cerium ammonium nitrate that has been oxidized to Ce(IV) by an oxidant.
5. The method according to claim 2, characterized in that, The alkaline solution in step (2) is at least one of the following: a solution of hydroxide corresponding to an alkali metal or alkaline earth metal, ammonia, ammonium carbonate, ammonium bicarbonate, and urea; the solution temperature in step (2) is controlled at 40–80°C during the titration process.
6. The method according to claim 2, characterized in that, In any step (1) to (4), a surfactant is added to adjust the pore structure of the material. The surfactant is added to the mixed precursor salt solution, or to the alkaline solution, or to the suspension after precipitation, or to the suspension after aging, or to the filter cake obtained by filtration of the suspension after aging. The surfactant is at least one of anionic surfactant, cationic surfactant and nonionic surfactant. The amount of surfactant added is 20% to 55% of the mass of the CeO2-ZrO2-based oxygen storage material to be prepared.
7. The method according to claim 2, characterized in that, Ce prepared by coprecipitation or heterogeneous nucleation according to any one of claims 1 to 6 x Zr 1-x Heterogeneous particles are introduced into the O2 material; the heterogeneous particles are those that are compatible with the target Ce. x Zr 1-x Ce with different compositions and structures of O2 materials x Zr 1-x O2, or at least one of Al2O3, SiO2, perovskite, spinel nanocrystals.
8. The method according to claim 7, characterized in that, The method of introducing heterogeneous particles by coprecipitation is as follows: in step (1), Ce x Zr 1-x The precursor of heterogeneous particles is added to the O2 mixed precursor salt solution; the method of introducing heterogeneous particles by heterogeneous nucleation is to use the fresh Ce obtained in step (5). x Zr 1-x Using O2 material as a heterogeneous core, the heterogeneous core is mixed with a heterogeneous precursor salt solution corresponding to the heterogeneous particles to be introduced, resulting in a mixed suspension. An alkali solution or complexing agent is added to the mixed suspension to precipitate the heterogeneous precursor salt ions onto the heterogeneous core. The resulting precipitate or gel is calcined at 750–1000°C to obtain the final Ce modified heterogeneous particles. x Zr 1-x O2 material.
9. The method according to claim 8, characterized in that, In the method of introducing heterogeneous particles through heterogeneous nucleation, the alkaline solution is one or more of ammonia, sodium hydroxide, ammonium carbonate, ammonium bicarbonate, and urea; the complexing agent is one or more of citric acid, ethylenediaminetetraacetic acid, and oxalic acid.
10. The method according to claim 2, characterized in that, Ce prepared by the method according to any one of claims 1 to 9 x Zr 1-x O2 materials modulate Ce through surface modification x Zr 1-x The surface modification of O2 involves surface doping with a surface additive, surface etching, or atmospheric treatment. The surface additive is at least one of alkaline earth metals, transition metals, Y, or elements with atomic numbers 57-71. The surface etching is one of acid etching, alkaline etching, or plasma etching. The atmospheric treatment is either inert atmosphere treatment or reducing atmosphere treatment, or a combination of both. The surface modification can be performed on Ce2 prepared under any of the above conditions. x Zr 1-x Performed on O2.