One-step synthesis and characterization of ZrO2-WOx prepared by hydrothermal method at autogenous pressure
One-step synthesis and characterization of ZrO2-WOx prepared by hydrothermal method at autogenous pressure
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DOI：
10.1039/b208335c
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发表时间：
2003-01-01
影响因子：
--
通讯作者：
Vázquez, A
中科院分区：
文献类型：
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作者：
Armendáriz, H;Cortes, MA;Vázquez, A
在高压釜中，在自生压力下，在 145 至 225 ℃ 的温度范围内，水热法制备一系列 ZrO2-WOx 样品 24 小时。通过元素分析、X射线衍射、氮物理吸附以及结构和吸附吡啶的FT-IR光谱对材料进行了表征。还对 X 射线衍射图进行了 Rietvelt 精修。在低至 145 摄氏度的合成温度下检测到结晶产物的形成。在 145 摄氏度下处理时，纯羟基氧化锆凝胶产生亚稳态 t-ZrO2 (63%) 和 m-ZrO2 (37%) 氧化锆相的混合物。当将钨（15 wt.%，以 WO3 计）添加到合成混合物中时，仅检测到 t-ZrO2 的非晶相。水热处理引起的t-ZrO2 相的结晶和t-ZrO2 到m-ZrO2 相变均因钨的存在而被延迟。这样在145℃的水热条件下制备了309m(2)g(-1)的微晶ZrO2-WOx。随着合成温度的升高，材料逐渐变得更加结晶。在225℃下，获得了结晶良好的材料（79%的t-ZrO2相和21%的m-ZrO2相）。有趣的是，两个相的微晶尺寸差别不大，t-ZrO2 和 m-ZrO2 分别为 15.6 和 13 nm。在所有样品中，与 WOx 物质相关的晶相均未通过 XRD 明确鉴定出来。 W 促进的氧化锆的 FT-IR 光谱显示在 943 cm(-1) 处存在非钨促进的 ZrO2 中不存在的谱带，这归因于八面体配位钨物质的 WLO 拉伸模式。由于 ZrO2 结构的晶格参数不会因钨的存在而改变，因此 WOx 物质必须高度分散并与 ZrO2 表面牢固结合。在较高温度（560、700和800摄氏度）下进行合成后煅烧处理导致这些分散的钨物质烧结，并形成体积更大的氧化钨物质，其特征在于970和1100 cm(-1)处有两个FT-IR振动带。
A series of ZrO2-WOx samples was hydrothermally prepared in an autoclave at autogenous pressure in a range of temperatures from 145 to 225 degreesC for 24 h. The materials were characterized by elemental analysis, X-ray diffraction, nitrogen physisorption and FT-IR spectroscopy of both structure and adsorbed pyridine. The Rietvelt refinement of the X-ray diffraction patterns was also performed. The formation of crystalline products was detected at synthesis temperatures as low as 145 degreesC. Pure zirconium oxihydroxide gel yielded a mixture of metastable t-ZrO2 (63%) and m-ZrO2 (37%) zirconia phases when treated at 145 degreesC. When tungsten (15 wt.% as WO3) was added to the synthesis mixture, only an amorphous phase of t-ZrO2 was detected. Both the crystallization of t-ZrO2 phase and the t-ZrO2 to m-ZrO2 phase transformation, caused by hydrothermal treatment, were retarded by the presence of tungsten. In this way a microcrystalline ZrO2-WOx of 309 m(2) g(-1) was prepared under hydrothermal conditions at 145 degreesC. The material becomes progressively more crystalline with increasing synthesis temperature. At 225 degreesC a well-crystallized material (79% of t-ZrO2 and 21% of m- ZrO2 phases) was obtained. Interestingly, the crystallite sizes of both phases were not too different, 15.6 and 13 nm for t-ZrO2 and m-ZrO2 respectively. In all the samples, crystalline phases associated with WOx species were not unambiguously identified by XRD. FT-IR spectroscopy of W-promoted zirconia showed a band at 943 cm(-1) not present in non-tungsten-promoted ZrO2, which was attributed to the WLO stretching mode of octahedrally coordinated tungsten species. Since the lattice parameters of the ZrO2 structure were not modified by the presence of tungsten, the WOx species must be highly dispersed and strongly bound to the ZrO2 surface. Post-synthesis calcination treatment at higher temperatures (560, 700 and 800 degreesC) brought about sintering of these dispersed tungsten species and the formation of a more bulky tungsten oxide species characterized by two FT-IR vibration bands at 970 and 1100 cm(-1).