The redox properties of titania films grown by ALD on
SBA-15, a
silica-based mesoporous material, were characterized as a function
of thickness (that is, the number of ALD cycles used).29Si CP/MAS NMR helped to identify the nature of the surface species
that form in the initial stages of deposition, and infrared absorption
spectroscopy was used to follow the transition from silica to titania
surfaces. The reducibility of the titania sites by CO and H2was studiedex situusing EPR andin situwith ambient-pressure XPS. It was determined that the titania ALD
films are amorphous and easier to reduce than crystalline titania
and that the reduction is reversible. A transition in the nature of
the surface was also observed, with unique mixed Si–O–Ti
sites forming during the first few ALD cycles and a more typical titania
surface progressively developing as the film grows in thickness.