Migration of nickel and titanium oxide species as studied by in situ scanning transmission electron microscopy

Abstract

The interactions between nickel and titania were studied by in situ scanning transmission electron microscopy during treatments in hydrogen at temperatures near 1000 K. Large nickel particles (e.g., 100 nm) were observed to create pits in the titania films on which they were supported. In addition, the titania films, originally rutile TiO 2, were converted to Ti 4O 7 during treatment in hydrogen at ca. 1000 K. It is suggested that the nickel facilitates reduction of titania in close proximity to the metal particles, thereby leading to the formation of pits in the titania support. The reduced-titania species removed from the support during this process migrate onto and/or into the nickel particles. Evidence is presented that indicates the migration of both nickel and titania may be involved in this process. This mode of migration may be a general phenomenon for metals on reducible supports. The resulting presence of titania species on the metal surface is thought to be responsible for the occurrence of so-called “strong metal-support interactions”