铈铁固溶体的制备及表征

【作者】 王海利；

【导师】 古映莹；

【作者基本信息】 中南大学 ， 无机化学， 2010， 硕士

【摘要】 在控制产物颗粒的大小、形貌和粒度分布方面,模板法具有独特优势而成为制备纳米材料的重要途径。软模板更是因为其胶体体系所组成的有序的聚集体,可以提供动态平衡的空腔,且孔道的大小和形状可以随实验条件的不同而变化,因此成为材料制备的先进技术。本文分别采用水热法和水热模板法(分别以非离子表面活性剂PEG-4000和阴离子表面活性剂SDBS为模板剂)制备了高比表面积、具有介孔结构的铈铁固溶体,探讨了制备条件对比表面积、孔结构和热稳定性的影响,并对产物进行了XRD、FT-IR、TEM、H2-TPR和比表面测试等检测。采用水热法制备产物时,主要考察了不同Ce/Fe物质的量的比和共沉淀温度对产物晶相、表面性能和还原性能的影响以及产物的热稳定性。XRD结果表明,不同Ce/Fe物质的量的比对产物的晶相有较大的影响。当x=0.9、0.8、0.7、0.6时,可以合成单一物相的铈铁固溶体；而当x=0.5时,得到的是含有八边形FeO(OH)杂相的铈铁固溶体；BET检测结果表明,共沉淀温度对产物的比表面积有较大的影响。当共沉淀温度为10℃时,合成的产物具有较大的比表面积,为143.7m2·g-1。随着共沉淀温度的升高,产物的比表面积有下降的趋势；TEM检测结果表明,所合成的Ce0.9Fe0.1O2产物具有蠕虫状介孔结构；H2-TPR结果表明,所得的产物具有较好的还原性能。以PEG-4000为模板剂,采用水热法制备铈铁固溶体时,主要考察了其用量、水热温度对产物比表面积的影响和溶液的pH值、水热对产物晶相的影响以及产物的热稳定性。XRD检测结果表明,pH值对产物的晶相有较大的影响。当pH为10(±0.05)时,可以合成单一物相的铈铁固溶体；而当pH为9(±0.05)时,得到的是含有杂相的铈铁固溶体。水热温度对产物的晶相几乎没影响,但随着水热温度的升高,产物的结晶程度越来越好；小角度XRD检测结果表明,所得产物具有规整有序的介孔结构；BET检测结果表明,PEG-4000的用量和水热温度对产物的比表面积有较大的影响,当PEG-4000/([Ce]+[Fe])的物质的量的比为0.3、反应温度为150℃时,制得的产物有较大的比表面积,为160.6 m2·g-1；TEM检测结果表明,所合成的产物Ce0.9Fe0.1O2具有蠕虫状介孔结构；FT-IR检测结果表明,表面活性剂PEG-4000与前驱体发生了协同作用,经过500℃煅烧后,产物中的表面活性剂已基本被除去。但产物的热稳定性较差,经过700℃高温煅烧后1h,产物的孔结构发生了严重坍塌,比表面积减小为43.2m2·g-1。以SDBS为模板剂,采用水热法制备铈铁固溶体时,主要考察了SDBS的用量对产物比表面积及热稳定性的影响。BET检测结果表明,SDBS用量对产物Ce0.9Fe0.1O2的比表面积有较大的影响,当SDBS/([Ce]+[Fe])的物质的量的比为0.4时,合成的产物具有较大的比表面积,为169.7 m2·g-1；而且产物具有较为均一的孔径分布,其平均孔径为4.5nm;FT-IR检测结果表明,表面活性剂SDBS与Ce(OH)3和Fe(OH)3乳胶发生了协同自组装作用,经过500℃煅烧后,产物中的表面活性剂仍有残余；TEM检测结果表明,产物Ce0.9Fe0.1O2具有蠕虫状介孔结构；产物的热稳定性较好,经过700℃高温煅烧后1h,产物的孔结构发生了部分坍塌,比表面积减小为77.8 m2·g-1;H2-TPR检测结果表明,产物的比表面积越大,其储氧量越大,低温还原性能越好。更多还原

【Abstract】 The template method has become an important way to prepare nanomaterials for its unique superiority in controlling the granule’s size, the appearance and the grain-size distribution. Especially, the soft template method, which provides the cavity of dynamieal equilibrium and the passageway’s size and the shape enhanging with the experimental condition, becomes the preponderant way to prepare nanomaterials. In this text, Mesoporous cerium-iron solid solution with fluorite cubic structure and high specific surface area was prepared by the hydrothermal method and hydrothermal method with nonionic surfactant polyethylene glycol (PEG) and sodium dodecyl benzene sulfonate(SDBS) as templates. The influence of synthesis parameters on BET, pore structure and thermal stability were investigated.The samples were aslo characterized by XRD, FT-IR, H2-TPR, TEM and BET.Hydrothermal method was used to prepare CexFe1-xO2 solid solution. The influence of the molar ratio of Ce/Fe and coprecipitation temperature on specific surface area, crystal phase and reduction performance are investigated. The XRD pattem show that the molar ratio of Ce/Fe has significant influence on phase component. The solid solution with single phase could be obtained When x=0.9,0.8,0.7,0.6 while the samples with a impurity phase of octagon FeO(OH) were prepared when x=0.5. The BET results show that coprecipitation temperature have influence on specific surface area. The prepared sample’s specific surface area is of 143.7 m2·g-1 at an coprecipitation temperature of 10℃(±0.05). With the temperature increasing, the sample’s specific surface area decreases. The TEM images show that the as-prepared sample Ce0.9Fe0.1O2 is of worm-like mesoporous structure. The H2-TPR results show that the as-prepared sample has a better reducibility.Under the system that using PEG-4000 as template, the influence of the amount of PEG-4000, hydrothermal temperature on specific surface area, the influence of pH value and temperature on phase were investigated. The solid solution with single phase could be obtained when pH value is about 10(±0.05) while the samples with a impurity phase were prepared when pH value is 9(±0.05). On the contrary, the hydrothermal temperature has less influence on the phase of the sample, but with temperature increasing, the sample has a better crystallinity. The low-angle XRD results show that mesoporous structure of the sample is deposited homogeneously. The BET results show that PEG-4000 content and hydrothermal temperature have influence on specific surface area when the molar ratio of Ce/Fe is 0.3, hydrothermal temperature is 150℃, the prepared sample’s specific surface area is of 160.6 m2·g-1. The TEM images show that the samples of Ce0.9Fe0.1O2 possess worm-like mesopore. The FT-IR results show that PEG-4000 cooperated with inorganic precursor and the residual PEG-4000 can be removed by calcination at 500℃. The as-prepared samples possess poor thermal stability, the specific surface area decreased to 43.2 m2·g-1 and the pore collapsed dramatically after calcination at 700℃for 1 h.Under the system that using SDBS as template, the influence of the amount of SDBS on specific surface area and the sample’s thermal stability were investigated. The BET results show that SDBS’s content has great influence on specific surface area and when the molar ratio of Ce/Fe is 0.4, the as-prepared sample’s specific surface area is of 169.7 m2·g-1, meanwhile pore size distribution of the sample is relatively symmetrical and the average pore size is 4.5 nm. The FT-IR results show that SDBS self-assembly with Ce(OH)3 and Fe(OH)3. There is a little amount of SDBS left in sample. The TEM images show that the sample of Ce0.9Fe0.1O2 holds worm-like mesopore.The sample performs excellent thermal stability and the specific surface are decreased to 77.8 m2·g-1 after calcination at 700℃for 1h. The H2-TPR results show that the OSC and the calalytic performance of low-temperature is related to specific surface area.更多还原