Behavior of titanium(3+) centers in the low- and high-temperature reduction of platinum/titanium dioxide, studied by ESR

Reduction of Pt/Ti02 at 573 K leads to the formation of a Ti3+ ESR signal, which disappears after a subsequent evacuation at 573 K. Readmission of hydrogen at room temperature makes the signal reappear.Such a reversibility is not observed when reduction takes place at 773 K.These observations are explained by a spillover of hydrogen atoms under the formation of Ti3+ and OH-ions.During the high-temperature reduction the hydrogenated TiOz surface around the platinum is dehydrated and a Ti407 layer is formed, thereby inhibiting the reversibility.