Using density-functional theory, an analysis was made of the thermodynamic stability of partially reduced, protonated, hydroxylated, and chlorinated V2O5(001) surfaces under flue-gas conditions. These surfaces were characterized geometrically by using surface relaxation calculations and electronically through charge distribution and density-of-states analysis in order to understand the change in surface reactivity under various pressure and temperature conditions. The stoichiometric surface was found to be the most favourable termination under flue gas conditions but, at low oxygen partial pressures (i.e., ultra-high-vacuum conditions) and elevated temperatures, the partially reduced V2O5(001) surfaces with one or two vanadyl oxygen vacancies were found to be stable. A surface semiconductor-to-metal transformation took place upon the addition of oxygen vacancies indicated by a decrease in the band gap. Protonation of the V2O5(001) surface took place only at low oxygen partial pressures where the main source or sink of hydrogen atoms came from H2. The study of the thermodynamic stability of protonated surfaces and surfaces with dissociated water with both H– and OH– groups indicated that these surfaces were not stable under flue gas conditions. Chlorinated surfaces were not stable under the flue gas and the coverage conditions tested. Larger HCl concentrations or smaller coverages could lead to stable chlorinated structures. However, the small coverages required to represent the chlorine flue gas concentrations accurately would require much larger unit-cell sizes. From this work it was evident that the stoichiometric surface of V2O5 was the most stable under flue-gas conditions.

Surface Reactivity of V2O5(001): Effects of Vacancies, Protonation, Hydroxylation, and Chlorination. A.S.Negreira, S.Aboud, J.Wilcox: Physical Review B, 2011, 83[4], 045423