The use of quantum chemical approaches in the description of electronic pro
perties of a catalyst and in understanding the mechanism of catalytic react
ions is discussed. The electronic structure of vanadium pentoxide, V2O5, is
studied based upon the cluster model with ab initio DFT and semiempirical
INDO-type methods. Inter-atomic binding in vanadium pentoxide is determined
to be of a mixed ionic and covalent character. Convergence of the electron
ic properties with respect to the cluster size is achieved for clusters as
large as V10O31H12. Similar electronic parameters of the V10O31H12 cluster
in its idealized, bulk and optimized geometry are obtained. The effect of t
he second substrate layer on the electronic properties is found to be negli
gible. The calculations reveal differences in the catalytic properties betw
een structurally inequivalent surface oxygen centers and show the increased
local reactivity of bridging oxygens with respect to the electrophilic adp
articles. The results of the adsorption of hydrogen, treated as a probe rea
ction to model the first step in the selective oxidation of hydrocarbons at
structurally different oxygen sites, are compared with the adsorption/acti
vation of aliphatic (propene) and aromatic (toluene) hydrocarbons at the va
nadium pentoxide(010) surface. The H/H+ species adsorbs at the V2O5(010) su
rface always at oxygen sites forming stable surface hydroxyl groups. The de
tailed mechanism of H/H+ stabilization depends on the structural and electr
onic properties of the adsorption site. The strongest binding occurs with t
he oxygen O(c) bridging two ban vanadium atoms. These O(c) oxygens become q
uite mobile in presence of the H/H+ adparticle. Oxidation of propene and to
luene on V2O5(010) into the aldehyde species proceeds through the formation
of C-O bond with the bridging oxygen, abstraction of two hydrogen atoms fr
om the same carbon atom of CH3-group, and generation of two OH-surface grou
ps. (C) 1999 Elsevier Science B.V. All rights reserved.