How do Core–Shell Structure Features Impact on the Activity/Stability of the Co-based Catalyst in Dry Reforming of Methane?

Dry reforming of methane has been systematically investigated over a series of x-Co@SiO₂-y catalysts where x is the Co particle size ranging from 11.1 to 121.3 nm while y denotes the silica shell thickness ranging from 6.0 to 21.9 nm. Various techniques including TEM, XRD, H₂-TPR/-TPD, XPS, BET, O₂-TPO, TG, and H₂-TPSR-MS were employed to characterize physicochemical properties of catalysts. H₂-TPR and XPS results indicate that the core–shell interaction is dependent on the core size: the smaller the Co particle size is; the stronger the core–shell interaction. The investigations employing H₂-TRSR-MS and XPS on the spent catalysts demonstrated that a fraction of metallic Co was re-oxidized on a large-core catalyst such as 121.3-Co@SiO₂-72.2 during the reaction, and such oxidation leads to lower catalytic activity and stability. O₂-TPO results indicated that the catalyst with smaller core size caused significant coking. TG analysis together with TEM investigation on the used samples suggested that carbon deposition is notably core-size-dependent and responsible for deactivation of the small-core catalyst. Among various core–shell structured catalysts, 27.8-Co@SiO₂-14.3 showed superior activity and durability, owing to the well-balanced property between coking and anti-oxidation of Co cores.