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.