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[Display omitted] • The migration pathways and oxidation process of single V atom in UHV and oxygen condition are determined. • O 2 atmosphere would affect the stability and dynamic behavior of V atom and V 2 dimer greatly. • Surface and subsurface V atoms can be easily oxidized to VO x monomers under the condition of oxygen gas. • V 2 dimer is stable in UHV while can be easily decomposed and oxidized into VO x monomers under oxygen condition. The migration and oxidation of single V atom and V 2 dimer on the anatase TiO 2 (1 0 1) surface are systematically studied based on density functional theory (DFT) calculations. For a single V atom, migration on the surface is almost impossible at room temperature while diffusion between surface and subsurface is easy in ultra-high vacuum (UHV) conditon. Without O attraction, single V atom prefers to stay at subsurface interstitial sites. But in oxygen condition, the subsurface interstitial V atom will easily diffuse to the surface and be oxidized into VO n (n = 1–3) monomers. The V 2 dimer is dynamically stable on the TiO 2 (1 0 1) surface and favors to be embedded in the surface layer in UHV condition. However, it can be easily decomposed and oxidized into VO n monomers in the condition of O 2. Our results offer an deep insight for the formation mechanism of sublayer vadanium oxides on TiO 2 support, and will be instructive for synthesizing desired VO x /TiO 2 catalysts. [ABSTRACT FROM AUTHOR]

• Atomic structures of vanadia oxide clusters supported on anatase TiO 2 (1 0 1) surface are predicted. • The structures of vanadia oxide clusters show a coverage-dependent feature. • VO 3 supported on the anatase TiO 2 (1 0 1) surface possesses particularly high reactivity. • NH 3 can only be dissociated on VO 3 /TiO 2 (1 0 1) surface. The atomic structures of VO x clusters supported on anatase TiO 2 (1 0 1) surface (A(1 0 1)) at different coverages are explored based on an evolutionary method. The structures exhibit clear coverage-dependent feature. Unlike those supported on rutile TiO 2 surface, monomeric vanania clusters supported on anatase surface do not favor aggregation. At low coverage, monomeric clusters (VO 2 or VO 3) are the main products, while at higher coverage (≥0.25 ML) polymeric clusters become more popular. Using the hydrogenation energy and oxygen vacancy formation energy as descriptors, and the dissociation of NH 3 as example, the reactivity of each stable structure is studied. The results show that VO 3 /A(1 0 1) possesses particularly high reactivity, and the supporting of V 2 O 5 and V 3 O 6 clusters can also improve the chemical reactivity of A(1 0 1) surface. The molecular adsorption of NH 3 can be enhanced on all the supported V m O n /A(1 0 1) structures, while its dissociation can only occur on VO 3 /A(1 0 1), which implies that the one-site mechanism of the selective catalytic reduction (SCR) reaction of NO x with ammonia only acts at low coverage of vanadium oxide (<0.25 ML). [ABSTRACT FROM AUTHOR]