γ-Al_2O_3表面担载钒物种的紫外拉曼光谱

本文采用常规的等体积浸渍法制备了不同担载量的V2 O5 γ -Al2 O3担载氧化物催化剂 ,在水气存在的条件下分别使用不同的激发波长得到了相应的可见拉曼光谱和紫外拉曼光谱。结果表明在表面钒物种微弱水合的情况下 ,3 2 5nm波长紫外激光激发的紫外拉曼光谱由于部分的共振拉曼效应 ,仍然可以灵敏的检测到表面钒物种配位结构随担载量增加而发生的变化。低担载时表面钒物种主要以孤立状态存在 ,随担载量增加逐渐向聚合态结构过渡 ,当担载量超过钒在载体表面的单层分散容量时形成体相V2 O5晶体覆盖表面钒物种造成拉曼信号的减弱 ,由此可以从另一个角度判断表面单层分散容量。

UV Raman Characterization of Supported Vanadium Oxide Catalysts

V 2O 5/γ-Al 2O 3 catalysts are prepared through incipient impregnation with different Vanadia loading Raman spectroscopy characterization is employed at ambient condition with different excitation laser wavelength The results show that even under ambient conditions where surface supported vanadia species are partly hydrated, the coordination changes led by different vanadium loading can be detected sensitively with 325nm as the excitation wavelength This sensitivity is partly due to the resonance Raman effect The isolated monomeric VO 4 species at low loading are gradually replaced by the polymeric species with the increased vanadium loading, until the bulk V 2O 5 emerges when the monolayer surface coverage is exceeded Thus the UV Raman spectroscopy can provide a novel method to understand the structure of surface vanadium species and identify the surface monolayer density