TITANIA-MODIFIED HYDRODESULFURIZATION CATALYSTS .2. DISPERSION STATE AND CATALYTIC ACTIVITY OF MOLYBDENA SUPPORTED ON TITANIA ALUMINA CARRIER

A series of molybdena catalysts supported on titania-modified alumina carrier was characterized by X-ray diffraction (XRD), analytical electron microscopy (AEM), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR). The results show that the type of Mo6+ species depends upon the coverage of titania on alumina. The molybdenum atomic concentration was improved when most of the surface of alumina was occupied by titania. TPR profiles of molybdena/titania-alumina exhibit two peaks at 680-710 K and 1090-1100 K. The amount of hydrogen consumption in the TPR process increases with a rise in titania content, which suggests that titania promotes the reduction of molybdena to much lower valency. The XPS data is in agreement with the TPR results. The measurements of the activity of the catalyst in hydrodesulphurization (HDS) of thiophene and hydrogenation (HYD) of cyclohexene indicate that titania-modified alumina supports can improve the HDS primary activity of the catalyst.