Effect of the TiO₂ Reduction State on the Catalytic CO Oxidation on Deposited Size-Selected Pt Clusters

The catalytic activity of deposited Pt₇ clusters has been studied as a function of the reduction state of the TiO₂(110)-(1 × 1) support for the CO oxidation reaction. While a slightly reduced support gives rise to a high catalytic activity of the adparticles, a strongly reduced one quenches the CO oxidation. This quenching is due to thermally activated diffusion of Ti³⁺ interstitials from the bulk to the surface where they deplete the oxygen adsorbed onto the clusters by the formation of TiO_x (x ≃ 2) structures. This reaction is more rapid than the CO oxidation. The present results are of general relevance to heterogeneous catalysis on TiO₂-supported metal clusters and for reactions involving oxygen as intermediate.