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Cluster model studies on catalytic properties of vanadium pentoxide

100%

Witko M. , Tokarz R. , Hermann K.

tom Vol. 72, nr 7S

1565-1583

ZINDO cluster model calculation are performed to study the electronic structure and chemical reactivity of the V2O5(010) surface. Inter-atomic binding in vanadium pentoxide is determined to be of a mixed ionic and covalent character. The calculations reveal the difference in the catalytic propertoes between structurally inequivalent surface oxygen centers and show the increased local reactivity of bridging oxygens with respect to the electrophilic adparticles. Convergence of the electronic properties with respect to the cluster size is achieved for cluster as large as V10O31H12. The effect of the second substrate layer on the surface electronic properties is found to be negligile. Further, rather similar electronic parameters of the V10O31H12 cluster in its idealized, bulk and optimized geometry are obtained. The H/H(+) species adsorb at the V2O5(010) surface, always at oxygen sites, forming very stable surface hydroxyl groups. The strongest binding occurs with the oxygen O(c) bridging two bare vanadium atoms. These O(c) oxygens become quite mobile in presence of the H/H(+) adparticle. Allowing the surface oxygen to ralax during adsorption of H/H(+) leads to different adsorption scenarios depending on the surface oxygen site. At the vanadyl oxygen site a very stable and rigid hydroxyl group O(A)H is formed above the vanadium center. At the doubly coordinated oxygen site O(b) the adsorbate penetrates between two vanadyl groups to form a local O(b)H group, while at the O(c) site an O(c)H group is created (slightly above the surface O(c) position), where O-H binding is strongest. Weak initial interaction, between triply coordinated oxygen O(d,e) and the incoming H/H(+) species, leads to stabilizaton of the adsorbate near the closest vanadyl site resulting in a tilted O(a)H group instead of O(d) H or O(e)H.

Adam Bielański (1912 - 2016)

32%

Witko M.

nr 4