The structure and surface acidity of zirconia-supported tungsten oxides
The structure and surface acidity of zirconia-supported tungsten oxides
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DOI：
10.1023/a:1019041402892
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发表时间：
1998-01-01
影响因子：
2.8
通讯作者：
Chen, Y
中科院分区：
文献类型：
--
作者：
Ji, WJ;Hu, JQ;Chen, Y
采用BET、XRD、FT拉曼、Tian-Calvet微量热法以及XPS等手段研究了氧化锆负载氧化钨的结构和表面酸性。以可控的方式制备了三种不同晶型的ZrO2及其氢氧化物前体。结果发现，所用的起始原料和制备条件对所得ZrO2的结构有显着影响。氢氧化锆上的钨酸盐物种一般会促进氢氧化物前体向四方ZrO2的转变，而预煅烧ZrO2上的相同物种在煅烧过程中影响较小。初始浸渍单斜晶系、四方晶系和立方晶系ZrO2或间型和叔型ZrO2的氢氧化物前体制备的样品中存在体相WO3，而初始浸渍c-ZrO2的氢氧化物前体制备的样品中不存在结晶WO3。拉曼结果表明，三种不同的氢氧化锆或其各自的氧化锆上的表面钨酸盐在煅烧前具有相似的结构特征。表面氧化钨和一些 WO3 体相是最终样品中可检测到的钨物质，每种成分的比例很大程度上取决于制备历史和载体的性质。在氧化锆负载的氧化钨上产生非常强的酸性位点与氧化锆本身的晶型、氧化钨物种的类型以及表面氧化钨覆盖层和氧化锆之间的合作有关。强酸性位点可能会被剩余的钠离子杂质完全毒化，但并没有受到添加的钇成分的明显影响。结晶WO3似乎在建立强表面酸性方面并不重要。
The structure and surface acidity of zirconia-supported tungsten oxide are studied by using BET, XRD, FT Raman, Tian-Calvet microcalorimetry as well as XPS. Three different crystal forms of ZrO2 and their hydroxide precursors were prepared in a controllable way. It was found that the starting material and preparing conditions used have a significant effect on the structure of ZrO2 obtained. The tungstate species on zirconium hydroxide generally promote the transformation of the hydroxide precursor into tetragonal ZrO2, while the same species on the pre-calcined ZrO2 has less effect during calcination. A bulk-phase WO3 existed in the samples prepared by initially impregnating the monoclinic, tetragonal and cubic ZrO2 or the hydroxide precursors of m- and t-ZrO2, while no crystalline WO3 was present in the samples prepared by initially impregnating the hydroxide precursor of c-ZrO2. Raman results revealed that the surface tungstate(s) on three different zirconium hydroxides or their respective zirconia have similar structural features before calcination. The surface tungsten oxides and some WO3 bulk phase are the detectable tungsten species in the final samples, the ratio of each component is strongly dependent on the preparation history and the nature of the support. Creation of very strong acidic sites on the zirconia-supported tungsten oxide is related to the crystal form of zirconia itself, the type of tungsten oxide species, and the cooperation between the surface tungsten oxide overlayer and zirconia. The strong acidic sites can be completely poisoned by the remaining sodium ion impurities, but have not been appreciably influenced by added yttrium component..The crystalline WO3 seems of little importance in building up the strong surface acidity.