Publications Details
Ceramic catalyst materials
This project focuses on the modification of silica and alumina surfaces by titania and hydrous titanium oxide ion-exchange films, and the use of these modified materials as supports for MoS{sub 2} catalysts. FTIR studies of molybdena interaction with {gamma}-Al{sub 2}O{sub 3} demonstrate that at low loadings Mo interacts with the most basic hydroxyl groups, and that these hydroxyls are associated with tetrahedrally coordinated Al. Furthermore, hydrodesulfurization (HDS) activity as a function of Mo loading shows a maximum in specific activity with loading. The Mo species bound to tetrahedrally coordinated Al sites are therefore believed to be inactive for the HDS reaction. Only after the tetrahedral Al sites have completely consumed does molybdena adsorb on the alumina in a manner that leads to an active catalyst. According to this scheme, the activity of alumina supported MoS{sub 2} catalysts could be greatly improved by either titrating the tetrahedral Al sites with a modifier, or by using {alpha}-Al{sub 2}O{sub 3} which contains no tetrahedrally coordinated Al. HDS tests over MoS{sub 2} supported on both {alpha}-Al{sub 2}O{sub 3} and {gamma}-Al{sub 2}O{sub 3} modified by a titania film confirm this hypothesis. Neither support material gives rise to a maximum in activity with Mo loading, but rather exhibits a smooth decrease in activity with loading. Furthermore, for equivalent Mo loadings the activity of both of these support materials exceeds that of unmodified {gamma}-Al{sub 2}O{sub 3} due to the fact that no Mo is tied up in the inactive form. FTIR, XPS, and TEM are currently being used to determine whether the model can indeed account for the observed activity trends. Although the surface area of {alpha}-Al{sub 2}O{sub 3} is too low for use as a commercial catalyst, the titania coated {gamma}-Al{sub 2}O{sub 3} represents an important, practical improvement in support materials for hydrotreating catalysts.