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 photoemissio n (ARUPS) measurements were performed to examine properties of differently coordinated surface oxygens at the V2O5(010) surface, Calculations on embed ded 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 prese nt photoemission data for freshly cleaved V2O5(010) samples. Cluster derive d total and partial densities of stares (DOS, PDOS) can be used to identify differently coordinated surface oxygens. The PDOS referring to terminal (v anadyl) oxygens is localized near the center of the valence band whereas th e PDOS's of the different bridging oxygens yield a broad distribution cover ing the full energy range of the valence bands. The shape of the experiment al ARUPS curves for V2O5(010) is well reproduced by the cluster DOS. Thus, the most prominent central peak in the experimental spectrum can be assigne d to emission from terminal oxygen while the peripheral peaks at the top an d bottom of the valence energy region are characterized as mixtures of vana dium with bridging oxygen induced contributions. This interpretation forms a basis to get insight into microscopic features at the real V2O5(010) surf ace such as imperfections and adsorbate binding. The present study suggests that the different O 2sp derived peaks observed in the photoemission exper iment may be taken as monitors of the differently coordinated oxygens at th e oxide surface and can be used to study details of catalytic surface react ions in which these oxygens participate. (C) 1999 Elsevier Science B.V. All rights reserved.