Properties and identification of oxygen sites at the V2O5(010) surface:: theoretical cluster studies and photoemission experiments

Density functional theory cluster studies and angular resolved photoemission (ARUPS) measurements were performed to examine properties of differently coordinated surface oxygens at the V2O5(010) surface, Calculations on embedded clusters as large as V16O49H18 confirm the ionic character of the oxide. The computed width of the O 2sp dominated valence band region of V2O5 and the work function value of V2O5 (010) are in good agreement with the present photoemission data for freshly cleaved V2O5(010) samples. Cluster derived total and partial densities of stares (DOS, PDOS) can be used to identify differently coordinated surface oxygens. The PDOS referring to terminal (vanadyl) oxygens is localized near the center of the valence band whereas the PDOS's of the different bridging oxygens yield a broad distribution covering the full energy range of the valence bands. The shape of the experimental ARUPS curves for V2O5(010) is well reproduced by the cluster DOS. Thus, the most prominent central peak in the experimental spectrum can be assigned to emission from terminal oxygen while the peripheral peaks at the top and bottom of the valence energy region are characterized as mixtures of vanadium with bridging oxygen induced contributions. This interpretation forms a basis to get insight into microscopic features at the real V2O5(010) surface such as imperfections and adsorbate binding. The present study suggests that the different O 2sp derived peaks observed in the photoemission experiment may be taken as monitors of the differently coordinated oxygens at the oxide surface and can be used to study details of catalytic surface reactions in which these oxygens participate. (C) 1999 Elsevier Science B.V. All rights reserved.