Dispersion states and acid properties of SiO2-supported Nb2O5

• The dispersed process of Nb2O5 was completed by consuming surface hydroxyl groups of SiO2.
• XRD quantitative phase analysis is not applicable for oxides dispersing on amorphous support.
• The catalytic activity of Nb2O5/SiO2 is closely related to the dispersion state of SiO2.

Nb2O5/SiO2 samples were prepared by the incipient-wetness impregnation method using niobium oxalate aqueous solution. The microstructure and dispersion process of the niobia species supported on SiO2 were characterized by means of power X-ray diffraction (XRD), laser Raman spectroscopy (LRS), and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). The acid properties were investigated by the method of Hammett indicator and Pyridine adsorption infrared (Py-IR) spectroscopy. The results showed that the dispersion process of Nb2O5 was performed by consuming surface hydroxyl groups of the amorphous SiO2 support. The aggregation of niobia species led to the formation of microcrystalline particles, so that there was no a clear monolayer dispersion capacity for Nb2O5 supported on amorphous SiO2. Furthermore, the catalytic activities of the as-prepared samples were evaluated by the condensation reaction of iso-butene (IB) and iso-butyraldehyde (IBA) to form 2,5-dimethyl-2,4-hexadiene (DMHD). The catalytic activities of the as-prepared samples for the condensation and their acid properties were strongly affected by the dispersion states.

The acid amount and strength of Nb2O5/SiO2 samples varied with the increase of Nb2O5 loading. The catalytic activities of the as-prepared samples for the condensation and their acid properties were strongly affected by the dispersion states.Figure optionsDownload as PowerPoint slide