Solid-state NMR investigation of the 16/17O isotope exchange of oxygen species in pure-anatase and mixed-phase TiO2

Quantitative 17O MAS NMR investigation of the 16/17O isotope exchange on pure-anatase TiO2/A and mixed-phase TiO2/A + R with an anatase to rutile ratio of 1:1 has been performed. Evaluation of the exchange kinetics hints to a strong decrease of the activation energy of this reaction on mixed-phase TiO2/A + R material (61 (A) and 70 kJ/mol (R)) compared with pure-anatase TiO2/A (105 kJ/mol). Furthermore, a very rapid increase of the 17O MAS NMR signals of surface oxygen species indicates a preferred 16/17O isotope exchange at these sites and a subsequently exchange with 16O framework atoms in the anatase and rutile domains.