摘要
测定了MoO_3/γ-Al_2O_3、MoO_3/TiO_2、MoO_3/SiO_2的激光Raman谱。通过MoO_3/γ-Al_2O_3、MoO_3/TiO_2在吡啶吸附前后、氨水提取前后的谱图对比说明,单层分散的MoO_3,即特征峰为～950cm^(-1)的“二维聚钼酸”中钼的配位状态不是单一的。其中一种表面含钼物种(Mo-1)不吸附吡啶,不溶于氨水,不显示较强的表面酸性;另一种表面含钼物种(Mo-2)可吸附吡啶,溶于氨水,与催化剂的表面酸位密切相关.我们认为Mo-1为四面体配位的钼;Mo-2为八面体配位的钼。MoO_3/SiO_2中的MoO_3能100％被氨水溶去,其酸位数与表面Mo^(6+)数之比接近1,是由其中Mo-2的比例较高,载体与活性组分之间的相互作用较弱这两个因素所造成的。
The Laser Raman Spectra of MoO_3/γ-Al_2O_3, MoO_3/TiO_2, and MoO_3/SiO_2 have been measured. The spectra of MoO_3/γ-Al_2O_3 and MoO_3/TiO_2 were compared with those after adsorption of pyridine and with those after treatment with aqueous ammoniasolution. It can be seen that coordination states of Mo in monolayer dispersed MoO_3 (i.e. the twodimensional polymeric surface molybdenum species with its typical bond at around 950 cm^(-1)) are not the same. One kind of the surface molybdtenum species Mo-1 can not adsorb pyridine, and is insoluble in aqueous ammonia solution, which means that it is not the acidic site. Whereas the other kind of surface molybdenum species Mo-2 can adsorb pyridine, and is soluble in aqueous ammonia solution. So, this species is closely related with the surface acidity of the catalysis. It has been supposed that Mo-1 is tetrahedrally coordinated surface species, and Mo-2 is octahedrally coordinated species. The fraction of Mo-2 in MoO_3/SiO_2 is larger than that in MoO_3/γ-Al_2O_3, and the interaction between MoO_3 and support SiO_2 is weaker than that in MoO_3/γ-Al_2O_3, so that all the molybdena in MoO_3/SiO_2 is soluble and the ratio between acidic sites and surface Mo^(6+) approaches unity.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
1990年第3期227-231,共5页
Acta Chimica Sinica
基金
国家自然科学资基金
国家教委北京大学结构化学开放实验室课题006号
