Direct Evidence of Dynamic Metal Support Interactions in Co/TiO 2 Catalysts by Near-Ambient Pressure X-ray Photoelectron Spectroscopy
The interaction between metal particles and the oxide support, the so-called metal–support interaction, plays a critical role in the performance of heterogenous catalysts. Probing the dynamic evolution of these interactions under reactive gas atmospheres is crucial to comprehending the structure–performance relationship and eventually designing new catalysts with enhanced properties. Cobalt supported on TiO 2 (Co/TiO 2 ) is an industrially relevant catalyst applied in Fischer−Tropsch synthesis. Although it is widely acknowledged that Co/TiO 2 is restructured during the reaction process, little is known about the impact of the specific gas phase environment at the material’s surface. The combination of soft and hard X-ray photoemission spectroscopies are used to investigate in situ Co particles supported on pure and NaBH 4 -modified TiO 2 under H 2 , O 2 , and CO 2 :H 2 gas atmospheres. The combination of soft and hard X-ray photoemission methods, which allows for simultaneous probing of the chemical composition of surface and subsurface layers, is one of the study’s unique features. It is shown that under H 2 , cobalt particles are encapsulated below a stoichiometric TiO 2 layer. This arrangement is preserved under CO 2 hydrogenation conditions (i.e., CO 2 :H 2 ), but changes rapidly upon exposure to O 2 . The pretreatment of the TiO 2 support with NaBH 4 affects the surface mobility and prevents TiO 2 spillover onto Co particles.