Reactivity of (TiO2)N Clusters (N = 1−10): Probing Gas-Phase Acidity and Basicity Properties

Abstract

We present B3LYP calculations on a selection of small-size clusters with (TiO2)N stoichiometry (N = 1−10) built on previous works on TiO2 and SiO2 or derived by kinship with stable clusters of different sizes. Their reactivity is analyzed as a function of size and electronic structure. Gas-phase acidity is probed by H+ interaction with the oxygen sites, while basicity is tested by interaction of molecular NH3 with titanium sites. Correlation with size, topology, or electronic properties is observed for some systems. In general, the correlation with electronic levels (highest occupied and lowest unoccupied molecular orbitals, HOMO and LUMO) is good criteria of reactivity, although this is not always observed. The calculated values generally decrease with the size. The HOMO−LUMO gaps show oscillations and a general decrease with the size. Coordination of the active site influences both the levels of the frontier orbitals and their effect upon reactivity. The protonation testing the cluster basicity is found...