Abstrakt
Vanadia-promoted Rh catalysts and Rh-V alloys have shown enhanced reactivity in several heterogeneous catalytic processes. However, little is known about the role of electronic and geometrical effects of the alloy phase on the chemical reactivity.
In this article, we present experimental study on geometric and electronic structure of near-surface ordered alloys prepared by depositing V on Rh(110) surface and by subsequent annealing. STM, LEED, and XPD measurements were combined to determine the atomic structure.
The electronic influence of the subsurface vanadium on the Rh(110) surface was elucidated by means of core-level and angle-resolved valence band photoemission spectroscopy. The influence of the alloying on the interaction with gas molecules was probed by CO adsorption.
It was found that annealing at 973 K results in a (2 x 1) surface reconstruction of Rh surface atoms along [110] rows induced by subsurface vanadium. Annealing at higher temperatures induces diffusion of vanadium into deeper layers and formation of a (1 X 2) missing-row reconstruction, which is metastable at the bare Rh surface.
Photoemission spectroscopy revealed a rather small shift of the Rh valence band centroid upon alloying, which indicates only a small influence of the electronic effect on the reactivity. On the other hand, the (1 x 2) missing-row reconstruction brings about new adsorption sites and low-coordinated Rh atoms which are expected to significantly contribute to the enhanced reactivity of the Rh V alloy.