Oxygen Atom Exchange between Gaseous CO2 and TiO2 Nanoclusters

Isotopic exchange of oxygen atoms between gaseous (CO2)-O-18 and (TiO2)-O-16 nanoparticles has been studied using high-resolution Fourier transform infrared absorption and first-principles density functional theory calculations. The rate of formation of gaseous (CO2)-O-16 is found to be highly dependent on the nature of the titania sample, growing with increasing calcination temperature (i.e., with decreasing surface area) for both quasi-amorphous and crystalline samples. The unprecedented faster kinetics on high-surface-area titania made from Ti(IV) isopropoxide points at fundamental differences between this material and the usual nanocrystalline TiO2 (anatase). This is attributed to unique cluster-like structure of the noncalcined ex-isopropoxide titania. The experimental observations are rationalized by calculations of the activation barriers for oxygen exchange on a (TiO2)(10) cluster. The calculations predict that titanium nanoclusters with 4-fold coordinated titanium atoms have much lower barriers for O atom exchange than previously found for the oxygen defect sites on the single crystal (101) anatase surface.