负载型三氧化钼催化剂表面结构和表面酸位的激光Raman光谱研究

测定了MoO3/γ-Al2O3、MoO3/TiO2、MoO3/SiO2的激光Raman谱. 通过MoO3/γ-Al2O3、MoO3/TiO2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MoO3, 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. MoO3/SiO2中的MoO3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。

Laser raman spectroscopic investigation of the surface structure and acidic sites of supported molybdena catalysts

The laser Raman spectra of MoO3/g-Al2O3, MoO3/TiO2, and MoO3/SiO2 were measured. The spectra of MoO3/g-Al2O3 and MoO3/TiO2 were compared with those obtained after adsorption of pyridine and with those after treatment with aqueous NH3 solution The coordination states of Mo in monolayer dispersed MoO3 (i.e., the 2-dimensional polymeric surface Mo species with its typical bond at ~950 cm-1) are not the same. One kind of surface species (Mo-1) cannot adsorb pyridine and is insoluble in aqueous NH3 solution, which means that it is not the acidic site. The other surface species (Mo-2) can adsorb pyridine and is soluble in aqueous NH3 solution, which indicates that this species is closely related with the surface acidity of the catalysis. Mo-1 is probably a tetrahedrally coordinated surface species and Mo-2 is a octahedrally coordinated species. The fraction of Mo-2 in MoO3/SiO2 is larger than that in MoO3/g-Al2O3, and the interaction between MoO3 and SiO2 support is weaker than that in MoO3/g-Al2O3, so that all the MoO3 in MoO3/SiO2 is soluble and the ratio between acidic sites and surface Mo6+ approaches unity.