用MBS和XPS究负载型氧化铁催化剂载体与活性组分的相互作用

STUDIES ON INTERACTION BETWEEN SUPPORT AND ACTIVE COMPONENT IN SUPPORTED CATALYSTS BY MBS AND XPS

负载型催化剂具有高分散度、抗烧结、使用寿命长、机械性能好等优点,使用非常广泛.作为载体并非全是“惰性”的.载体与活性组分间常有不同程度的相互作用.这类催化剂载体与活性组分之间的相互作用能明显改变活性组分的颗粒大小、还原度以及催化。

Five supported samples, Fe2O3/HZSM-5 , Fe2O3/γ-Al3O3, Fe2O3/ α-Al3O3, Fe2O3/TiO2 and Fe2O3/SiO2, were prepared by impregnation method. Mossbauer spectra of these samples were recorded at room temperature ( 300 K), 250 K, 190 K and 77 K. We have found that spectra of all samples but SiO2 have exhibited quadruple splitting doublet at room temperature, and kept spectral doublet without magnetic splitting till temperature down to 77 K. For SiO2 supported one, it is doublet at room temperature, while exhibits magnetic splitting six peaks pattern at 77 K. Both XPS and MBS showed that active components of these samples are basically monolayer on supports except Fe2O3/SiO2. By using the Mossbauer spectra at different temperature we obtained a parameter θM, which can represent the relative intensity of interaction between active components and supports. Meantime, XPS gives the binding energy shifts of Fe 2P3/2 on different supports. These results pointed out that the order of interaction intensities of Fe2O3 on various supports obtained by XPS is the same as that from MBS, that is: Fe2O3/TiO2>Fe2O3/HZSM-5 >Fe2O3/γ-Al3O3 > Fe2O3/α-Al2O3>Fe2O3/SiO2. Computer fitting of reduced Fe 2P3/2 peaks in five samples reveals the influence of interaction between different supports and active components on reducibility of active component. The stronger the interaction, the more difficult the sample reduction. But it is not the only factor, structure of the supports should be considered also.