Reducibility of vanadium oxide species in MCM-41 1 Dedicated to Professor Lovat V.C. Rees in recogni
Reducibility of vanadium oxide species in MCM-41 1 Dedicated to Professor Lovat V.C. Rees in recogni
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MCM-41 中氧化钒物质的还原性 1 献给 Lovat V.C. 教授
DOI：
10.1016/s1387-1811(98)00088-2
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发表时间：
1998
影响因子：
5.2
通讯作者：
A. Zukal
中科院分区：
文献类型：
--
作者：
G. Grubert;J. Rathouský;G. Schulz;M. Wark;A. Zukal
通过(I)在水热合成过程中原位掺入V(记为V-MCM-41-SYN)、(Ii)在硅质MCM-41上化学气相沉积VOCl3(V-MCM-41-CVD)和(Iii)用钒基乙酰丙酮浸渍硅质MCM-41(V-MCM-41-IMP)制备了含钒MCM-41材料。从四次分辨反射的X射线衍射图中可以看出，该材料为有序的六方结构。从氮气吸附数据获得的无定形非多孔副产物的比例按顺序增加：V–MCM-41-imp≈5%<；V–MCM-41-cvd≈8%<；V–MCM-41-syn≈20%.UV/Vis漫反射光谱显示，由于所有材料在脱水状态下在30 000 cm−1以下没有吸收，因此主要是以四重四面体配位的单核VO氧化物。多核氧化钒物种的含量依次为：V-MCM-41-syn<；V-MCM-41-imp<；V-MCM-41-CVD。用原位DRS监测氢气还原成V的情况，可还原VV的比例按顺序递减：V–MCM-41-imp≈100%>；V–MCM-41-cvd≈67%>；V–MCM-41-syn≈14%.不可还原的物种被认为埋藏在无定形的副产品中或墙内。光电子能谱表明，可还原的氧化钒物种位于MCM-41结构的沟道中。对还原动力学的分析表明，一小部分多核VVoxide的还原速度要高出十倍。
Vanadium-containing MCM-41 materials were prepared by (i) in situ incorporation of V during hydrothermal synthesis (denoted as V–MCM-41-syn), (ii) chemical vapour deposition of VOCl3on siliceous MCM-41 (V–MCM-41-cvd), and (iii) impregnation of siliceous MCM-41 with vanadyl acetylacetonate (V–MCM-41-imp). A well-ordered hexagonal structure of the materials is revealed from XRD patterns exhibiting four resolved reflections. The fraction of amorphous non-porous by-product obtained from nitrogen adsorption data increases in the sequence: V–MCM-41-imp≈5%<V–MCM-41-cvd≈8%<V–MCM-41-syn≈20%. UV/vis diffuse reflectance spectroscopy (DRS) reveals predominantly mononuclear VVoxide in fourfold tetrahedral coordination owing to missing absorptions below 30 000cm−1in the dehydrated state for all materials. The content of polynuclear VVoxide species increases in the order: V–MCM-41-syn<V–MCM-41-imp<V–MCM-41-cvd. Reduction by hydrogen to Vredwas monitored by in situ DRS and the fraction of reducible VVdecreases in the sequence: V–MCM-41-imp≈100%>V–MCM-41-cvd≈67%>V–MCM-41-syn≈14%. The non-reducible species are assumed to be buried either in the amorphous by-product or inside the walls. Photoelectron spectroscopy reveals that the reducible vanadium oxide species are located in the channels of the MCM-41 structure. The analysis of the reduction kinetics points to a small fraction of polynuclear VVoxide reduced at a tenfold higher rate.