AVS 51st International Symposium
    Surface Science Monday Sessions
       Session SS1-MoA

Paper SS1-MoA4
CO Coupling Reaction on UO@sub2@(111)Single Crystal Surface: An Experimental and Theoretical Study

Monday, November 15, 2004, 3:00 pm, Room 210B

Session: Simulation and Theory of Adsorption
Presenter: S.D. Senanayake, The University of Auckland, New Zealand
Authors: H. Idriss, The University of Auckland, New Zealand
S.D. Senanayake, The University of Auckland, New Zealand
A.S.L. Soon, The University of Auckland, New Zealand
Correspondent: Click to Email
The unique electronic properties of UO@sub2@ makes it an ideal prototype material for investigation of new chemical pathways. Carbon monoxide molecules were found to selectively couple to C2 compounds over O-defected surfaces of UO@sub2@(111) single crystal. The most plausible reaction can be described by: 4CO + H@sub2@ -> C@sub2@H@sub2@ + 2CO@sub2@. This unique reaction is studied using temperature programmed desorption (TPD), X-ray Photoelectron Spectroscopy (XPS) and valence band, targeting surface intermediates and oxidation states of uranium and oxygen ions. Evidence of CO dissociation upon adsorption is seen by the disappearance of XPS lines due to U metal, the increase of those related to U@super4+@ and the formation of surface carbides. Preliminary steady state catalytic experiments on polycrystalline H@sub2@-reduced UO@sub2@ have further confirmed the selective pathway to acetylene and ethylene. Relativistic density functional theory (DFT) calculations have been performed using the Amsterdam Density Functional Theory for molecules and with BAND code for embedded clusters and periodic slab studies. Binding energies and conformations of CO adsorption on the surface are probed to offer a deeper understanding of surface energetics. The structures of interests were fully optimised with the inclusion of scalar relativistic effects, which were treated with the Zeroth-Order Regular Approximation (ZORA) formalism.