摘要
本文分别用X-射线光电子能谱(ESCA)、X-射线衍射仪(XRD)、正电子湮没谱(PASCA)及Faraday式磁天平等测试技术对WO_3在γ-Al_2O_3表面上的分散进行了研究.实验结果发现,用ESCA和XRD测定WO_3在γ-Al_2O_3表面上的最大单层分散量为27m%,相当于0.185g WO_3/100m^2.此结果与按WO_3在γ-Al_2O_3表面上作密置单层排布模型计算值极为吻合.而用PASCA和磁天平测定WO_3在γ-Al_2O_3表面上的最大单层分散量约为20m%,相当于64%的表面覆盖率,该值低于ESCA和文献[4,8]所测定的值.PASCA和磁天平的灵敏度比XRD和ESCA要高得多.因为PASCA可以在分子或原子水平上反映出物质结构的细微变化.从理论上讲Al_2O_3表面也不可能100%为WO_3所覆盖,因为Al_2O_3表面上不可避免会有一些"隐蔽"的角落和一部分WO_3进不去的微孔结构.XRD和ESCA测得的值可能是偏高的,而PASCA和磁天平测得的WO_3在γ-Al_2O_3表面上覆盖率为64%较为可信.
ESCA(electron spectroscopy for chemical analysis),XRD(X-ray diffraction),PASCA(positron annihilation spectroscopy for chemical analysis)and magnetic measurement technique were used to investigate the dispersion of WO_3 on γ-alumina.The results indicated that,by ESCA and XRD techniques,the maximum monolayer dispersion of WO_3 on γ-alumina is about 27m%,or 0.185 g WO_3/100m^2,which agrees well with the Calculated value based on closed monolayer dispersion model.However,the value obtained by PASCA and magnetic measurements,is 20m% or 0.120 g WO_3/100m^2,lower than that by ESCA and literature data,suqqesting that only 64% of the total surface of γ-alumina is occuppied by WO_3.PASCA and magnetic measurements(for paramagnetic materials,such as W and Mo)are more sensitive than XRD and ESCA.They are capable to reflect the surface states of the solids on atomic scale.In fact,100% coverage for WO_3(and also for MoO_3)on alumina surface is impossible to attained as there is always some'concealed conners'on alumina surface and some enter the micropore structure.The results by XRD and ESCA are probably too high.The 64% coverage for WO_3 on γ-alumina seems reliable.
出处
《石油学报（石油加工）》
EI
CAS
CSCD
北大核心
1990年第4期22-28,共7页
Acta Petrolei Sinica(Petroleum Processing Section)
