| AVS 66th International Symposium & Exhibition | |
| Surface Science Division | Tuesday Sessions |
| Session SS+2D+HC-TuM |
| Session: | Atom Manipulation and Synthesis/Oxide Surface Reactions & Flash Session |
| Presenter: | Kræn Christoffer Adamsen, Aarhus University, Denmark |
| Authors: | K.C. Adamsen, Aarhus University, Denmark J.V. Lauritsen, Aarhus University, Denmark S. Chiriki, Aarhus University, Denmark B. Hammer, Aarhus University, Denmark |
| Correspondent: | Click to Email |
Fundamental knowledge of catalytic processes for NOx removal (Selective Catalytic reaction, SCR) is important for improving existing catalysts and developing new. In the SCR cycle, NOx is known to react from gas-phase on adsorbed ammonia on a VOx/TiO2 based catalysts. It is well established that vanadium in the V+5-state is most catalytic active state, though is still debated whether it is a hydroxylated- or an unhydroxylated- species that is most active species. Here we investigate the structure of vanadium oxide (V2O5) before, under and after exposure of water.
By evaporation of Vanadium in an oxygen-rich atmosphere (10-6 mBar) on an anatase-TiO2 (101) substrate, we can create well-dispersed single V2O5 –clusters. Confirm the oxidation state of vanadium with X-ray Photo electron Spectroscopy (XPS) and image the size and structure with high resolution Scanning Tunneling Microscopy (STM). Prior to water exposure V2O5 –clusters appear predominately as elongated features extending across two bridging oxygen rows of the anatase-TiO2 (101) substrate. Utilizing the high scanning speed of the Aarhus STM we can follow the water induced restructuring of the clusters in situ. We observe a clear change in appearance of the vanadium oxide cluster, where a vanadium atom moves across on of the bridging oxygen rows of the a-TiO2 substrate. Removal of water causes another change in appearance, but re-exposure of water the previous appearance is restored. We therefor observe a reversible reaction with exposure and removal of water, however with several hour of pumping we cannot return to the initial state directly after evaporation.
Together with Theoreticians, we are able to suggest structure models of the interactions between the vanadium oxide and water. We are able to explain both the irreversible restructuring in the first water exposure and the reversible restructuring with re-exposure of water. Understanding the structure and it dynamical behavior under water exposure bring us closer to understand the catalyst under working conditions.