【摘要】 用X射线衍射（XRD）相定量外推法和X射线光电子能谱（XPS）峰强度比(Iw_4f/I_i-p)法定量测定了WO₃在硅胶表面的最大分散量,两种方法的结果一致,为1.8×10_-4克WO₃/米²(即4.6×10¹⁷W原子/米²)。表明WO₃在硅胶表面呈单层分散,但不是密置单层分散,WO₃在硅胶表面的单层覆盖率只有9%。更多还原

【Abstract】 Series of WO3/SiO2 catalysts, prepared by impregnating silica with solutions of ammonium tungstate and drying at 150℃ and then being calcined at 500, 550 and 600℃and X-ray photoelectron spectroscopy. By XRD quantitative extrapolation method, the experimental maximum dispersion capacities (the dispersion threshold value) of WO3 on silica with specific surface 371 m2/g for three series of WO3/SiO2 calcined at 500, 550 and 600℃ are found with the same value of 0.066 g WO3/g SiO2 (as an example for 550℃, see Fig. 2). The dispersion threshold value of WO3 on silica with specific surface 288 m2/g is 0.050 g WO3/g SiO2 (see Fig. 3). As considering the unit area, they are almost the same of 1.8×10-4 and 1.7×10-4 g WO3/m2 respectively. For the WP3/SiO2 calcined at 550℃ and silica with specific area 371 m2/g, the dispersion threshold value is found to be 1.8×10-4 g WO3/m2 (i.e.4.6×1017 W atom/m2, see Fig. 4) by XPS intensity ratio (IW4f/I9i2p) method. If WO3 dispersed on silica as a close-packed monolayer, the calculated maximum dispersion capacity would be 1.9×10-3 g WO3/m2, therefore, the experimental results show that WO3 disperses on silica surface as a monolayer with a coverage of 9 %, but not a close-packed monolayer.更多还原