46660-G5
Surface Science Investigation of MoS2 Nanoclusters Supported on TiO2 for a Fundamental Understanding of Hydrodesulfurization Catalysts
The formation of MoS2 clusters on TiO2 single crystal surfaces have been attempted by simultaneous or sequential vapor deposition of Mo in a sulifidizing H2S atmosphere. It was found that metallic Mo reacts with the TiO2 substrate and diffuses into sub-surface layers, at the same time sulfur reacts with the TiO2 surface forming titanium-oxysulfides. This behavior makes it difficult to synthesis a well-defined MoS2/TiO2 model catalyst system. The complex interactions between Mo and S and TiO2 may however shed new insight on the desulphurization reactions occurring on TiO2 supported MoS2 catalysts. In the second year of this project our studies will investigate these interactions in more detail.
In view of the apparent importance of the oxide support in the desulphurization reactions we turned to an alternative oxide system that is widely used in desulphurization of feedstock, i.e. ZnO. This system has turned out to be experimentally easier accessible and the progress in studying this system has been more rapid. We investigated the sulfur adsorption on two surface orientation of ZnO when exposed to H2S at 600 C under vacuum conditions. The adsorption was studied by synchrotron based photoemission and by scanning tunneling microscopy. The results of the compositional and electronic surface modifications have been already published in the Journal of Physical Chemistry C and a second publication is currently submitted for publication. These studies will also be intensified in the next year; in particular more detailed STM studies of the initial sulfide nucleation and growth on different ZnO surface orientations are planned.
