摘要
用XRD,XPS研究了V_2O_5在γ-Al_2O_3,SiO_2,TiO_2等载体上的分散状态,测定了最大分散容量。结果表明,V_2O_5在γ-Al_2O_3和SiO_2上能形成亚单层分散,分散容量分别为理论单层量的60％和45％;V_2O_5在TiO_2上优先形成单层,然后形成多层结构。V_2O_5在γ-Al_2O_3上分散可使表面酸性有所增加;V_2O_5在SiO_2上分散使表面酸性剧增,酸位数和表面V_(5+)的摩尔比高达0.5左右;V_2O_5在TiO_2上的负载不增加体系的表面酸性。对负载钒的分散状态及其存在形式进行了讨论。
The dispersion of V2O5 on γ-Al2O3, SiO2 and TiO2 has been studied by XRD and XPS. The maximum dispersion capacities have been determined. The results indicate that V2O5 can disperse on γ-Al2O3 and SiO2 as a sub-monolayer. The dispersion capacities are 60% and 45% of theoretical monolayer capacity respectively. On TiO2 surface, V2O5 initially disperses as a monolayer which subsequently develops into a multilayer structure. V2O5 dispersed on γ-Al2O3 causes a moderate increase in surface acidity, but V2O6 increases the surface acidity on SiO2 rather dramatically, the mole ratio between acidic centers and surface-bound V5+ is found to be as high as 0.5 for V2O6/SiO2. No increase in surface acidity is observed for the V2O5/TiO2 system. On the basis of the surface acidity studies, coupled with XRD and XPS analysis, the dispersed states of V2O5 on the supports are deduced and the possible structures are discussed.
基金
国家自然科学基金
关键词
负载型
催化剂
分散容量
表面酸性
supported V_2O_5 catalyst,dispersion capacity,surface acidity
