Molecular Design and In Situ Spectroscopic Investigation of Multilayered Supported M1Ox/M2Ox/SiO2 Catalysts
نویسندگان
چکیده
The group 5-7 transition metal oxides (V2O5, CrO3, MoO3, WO3, and Re2O7) were anchored on a surface modified SiO2 support containing surface alumina, zirconia, and titania species prepared via incipient wetness impregnation of soluble precursors and calcination. The molecular and electronic structures of these “multilayered” supported M1Ox/M2Ox/SiO2 catalysts were characterized with in situ Raman and UV-vis DRS spectroscopies under dehydrated conditions to provide insights into the interactions between the metal oxide overlayer (M1Ox) and the surface oxide modifiers (M2Ox) on the silica support. The supported M1Ox transition metal oxides preferentially coordinate to the surface M2Ox modifiers over exposed SiO2 support sites and are present as isolated surface M1Ox species. Although the molecular and electronic structures of monoxo surface OdVO3 and trioxo surface (Od)3ReO species are not appreciably perturbed by the surface modifiers, the group 6 surface CrOx, MoOx and WOx species are significantly altered by the presence of the surface M2Ox additives. The monoxo [OdMO4]/dioxo [(Od)2MO2] ratio of the silica-supported group 6 metal oxides is found to be controlled by the surface modifiers. The electronic structures of the group 6 surface metal oxides exhibit fewer LMCT transitions in the UV-vis spectra and higher Eg values in the presence of the surface M2Ox modifiers. Thus, both the molecular and electronic structures of the dehydrated group 6 surface metal oxides on SiO2 supports can be tuned with the addition of surface oxide modifiers.
منابع مشابه
Surface chemistry and reactivity of well-defined multilayered supported M1Ox/M2Ox/SiO2 catalysts
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