【摘要】 应用LRS、XRD、UV-DRS和TPR技术对负载氧化钨催化剂进行了表征.实验结果表明,WO₃在γ-Al₂O₃、TiO₂、SnO₂和ZrO₂载体表面高度分散直至形成完全覆盖单层;但在SiO₂表面WO₃难以分散.拉曼光谱是鉴别表面分散态和晶相WO₃的有力手段.对WO₃在表面单层覆盖的样品,表征表面 钨氧物种的拉曼振动频率的高低因载体而异.载体使表面钨氧物种稳定,抑制其还原并改变其还原进程.钨氧物种在载体表面的配位状态取决于负载量和载体的结晶结构.表面钨氧物种的拉曼频率和TPR还原峰温的高低与WO₃和载体之间相互作用的强弱有关.更多还原

【Abstract】 Five series of supported WO3 catalysts, prepared by impregnation method, have been studied by LRS, UV-DRS,XRD, and TPR methods.The major Raman bands of WO3 are located at 806, 712 and 272cm-1 and have been assigned to the W=O stretching, bending and W-O-W deformation vibration respectively. For WO3 supported on TiO2, ZrO2 and SnO2, as the loading is lower than or equal to the close-packed monolayer coverage, no crystalline WO3 could be detected by XRD and the Raman results show only a broad band at 934-978cm-1 attributed to the surface tungsten oxospecies. As the loading is higher than the monolayer coverage, the XRD data and Raman spectra indicate the appearance of bulk WO3 and the band at 934-978cm-1 is still observable but slightly shifts to higher frequency. For WO3 supported on SiO2, while the loading is much lower than the monolayer coverage, the characteristic Raman bands of crystalline WO3 already appear, and this result is consistent with the XRD data. For WO3/γ-Al2O3 at monolayer coverage no crystalline phase can be detected by XRD but the Raman bands of crystalline WO3 appear.The above results reveal that for γ-A12O3, TiO2, SnO2 and ZrO2 supports, owing to the relevant strong interactions, WO3 on the support surface is highly dispersed until the close-packed monolayer coverage is acheived, while for SiO2 support, WO3 is poorly dispersed, and LRS isa very sensitive technique for distinguishing highly dispersed and crystalline structural tungsten oxide on the support.UV-DRS results show that only octahedral oxospecies appear on the TiO2 and SnO2 surfaces even at very low WO3 coverage, while on SiO2 and ZrO2, both tetrahedral and octahedral oxospecies exist.From the TPR results it can be concluded that the reduction of bulk WO3 proceeds through intermediate tungsten oxidation states.The support surface stabilizes the dispersed tungsten oxospecies and substantially suppresses its reduction and changes the reduction process as well.The Raman shifts of the surface species and the Tm values of the TPR peak at monolayer coverage correlate with the interaction between WO3 and support. The strength of the WO3/support interaction increases in the following order: WO3/SiO2, WO3/ZrO2, WO3/SnO2, WO3/TiO2, WO3/γ-A12O3.更多还原