NiO在TiO_2载体表面的分散状态

NiO DISPERSION ON TITANIA SURFACE

采用X-光多晶衍射、透射电子显微镜、选区电子衍射、X-光光电子能谱、俄歇电子能谱等实验方法研究了NiO/TiO_2体系,表明NiO在低载量范围内以单层形式分散在载体TiO_2表面,当NiO的载量超过一定限度时,则除了单层分散之外,还出现多余的晶相NiO.XRD相定量外推法测定得到NiO在TiO_2表面的最大分散量(分散阈值)为0.097g NiO/100m^2TiO_2,XPS和AES峰强度比的测定得到与以上描述相吻合的结果.

NiO/TiO2 supported catalyst has been investigated by X-ray diff raction ( XRD ) , Transmission Electron Microscopy ( TEM ),High Ener gy Electron Diffraction ( HEED ), X-ray Photoelectron Spectroscopy ( XPS ) and Auger Electron Spectroscopy ( AES). A series of NiO/TiO2 samples was prepared by impregnation and calcined at 450℃ for 3 h. The NiO loading amout of NiO/TiO2 samples is from 0.02 to 0.40 g NiO/g TiO2, and the specific surface of TiO2 (Anatase)used is 86 m2/g. XRD patterns ( Fig.1 ), TEM graphs ( Fig.3 ) and HEED patterns ( Fig.4 ) show qualitatively that the crystalline NiO in the NiO/TiO2 samples can only be detected as the NiO loading is more than a certain value. The dispersion threshold (i.e. the experimental maximum dispersion capacity ) for NiO on TiO2 determined quantitatively by XRD from the amount of detectable crystalline NiO is 0.083 g NiO/g TiO2 or 0.097 g NiO/100 m2 TiO2 ( see Fig.2 ) . From the plot of the AES and XPS peak intensity ratios of I(Ni L3M45M45)/I(Ti2p3/2) as a function of NiO loading (see Fig.6), the turning point is at 0.08g NiO/g TiO2 as well, which agrees with the value obtained from XRD determination. According to a close-packed monolayer model the dispersion capacity for NiO on TiO2 should be 0.18 g NiO/100 m2 TiO2. Therefore NiO is dispersed on TiO2 carrier as a submonolayer with a coverage 6=0.54, rather than a close-packed monolayer.