Electronic Structure of Unsaturated V2O5(001) and (100) Surfaces: Ab Initio Density Functional Theory Studies

Abstract

Vanadium oxides based materials are well known to play an active role as catalysts in many chemical processes of technological importance like for example hydrocarbon oxidation reactions or selective catalytic reduction of NO x in the presence of ammonia. Usually the (010) surface is pointed out as the most important, however one has to underline that other low-indices surfaces are by far less studied. In the present study the electronic structure of V 2 O 5 (001) and (100) surfaces are determined by ab initio DFT methods using gradient-corrected RPBE exchange-correlation functional. Detailed analyses of the electronic structure of each cluster are performed using charge density distributions, Mayer bond orders, electrostatic potential maps, character of frontier orbitals, and density of states (total as well as partial, atom projected). Results of the calculations show that overall negative charge of the surface oxygen sites scales with their coordination independent of the surface orientation. Terminal oxygen O(1) is charged the least negatively while doubly coordinated atoms -O(2) and O e (2) have charge twice as large. This indicates that bridging (for (001) and (100) netplanes) and edging (only for (001) netplane) oxygen sites are more nucleophilic than terminal vanadyl sites, which becomes important in view of the reactivity of the different sites for surface chemical reactions. Vanadium atoms present at these surfaces are positively charged (electrophilic) and may play a role of electron acceptors. The unsaturated surfaces show a strong tendency to surface relaxation that manifest by large relaxation energies.

Reconstruction of Low-Index α-V2O5 Surfaces

“…These surfaces have been studied with DFT before, and the surface energy, 23 the electronic structure, 24 oxygen-vacancy formation energy, 25 and the adsorption energy of hydrogen, 25 water, 26 and ammonia 27 have been calculated. Those calculations were based on a surface structure with bulk periodicity, and as a result the surface geometry was very similar to that of the bulk.…”

Vanadium pentoxide (V2O5): A van der Waals density functional study

“…The α-phase of V 2 O 5 has a layered structure, illustrated in Figure 1. The bonds within the layers are strong while the interlayer binding is long-ranged and weaker and for this reason the material is easy to cleave in the plane perpendicular to c. O 5 has previously been studied with DFT by a number of groups using GGA [4,5,6,7,8,9] or by adding (semi-)empirical vdW-terms to GGA calculations [9]. Here our focus is on the vdW-DF method rather than on the material V 2 O 5 itself.…”

Elementary steps of the catalytic NOx reduction with NH3: Cluster studies on reactant adsorption at vanadium oxide substrate

“…(It should be mentioned in passing that surface reduction can also occur at vanadium pentoxide surfaces which are terminated along directions other than (010) and result in electronically unsaturated local regions considered previously. 35,75 ) Overall, most of the reactants, hydrogen, nitrogen, NO, NH, and NH 2 , bind quite strongly near all surface oxygen vacancy sites of the V 2 O 5 (010) substrate where they stabilize in positions formerly occupied by the oxygen. This substitutional adsorption geometry results in local surface relaxation where, due to binding with the adsorbate, the vanadium and oxygen atoms near the oxygen vacancy move towards their initial positions at the surface before the vacancy was created.…”