ROLE OF HYDROGEN IN THE MOBILITY OF PHASES IN NI-TIOX SYSTEMS

The role of hydrogen in the mobility of Ni and titanium suboxide phases in NiTiOx systems has been investigated by means of XPS and ISS. Two different systems have been examined, a composite NiTiOx material formed by large Ni particles (ca. 35 nm) embedded in a nonstoichiometric titanium oxide matrix and a Ni foil with evaporated TiOx species. Heating at 773 K leads to diffusion of the TiOx species into the Ni foil, a process which is strongly enhanced in the presence of H2. In a similar way, heating the NiTiOx composite in H2 at the same temperature results in a redistribution of the Ni atoms through the defective titanium oxide lattice. This hydrogen-enhanced diffusion of the TiOx and Ni species is discussed in relation to the SMSI state and other related phenomena occurring during the activation in H2 of Ni/TiO2 catalysts. © 1991.