Direct observation of the evolving metal–support interaction of individual cobalt nanoparticles at the titania and silica interface

Abstract

Understanding the metal-support interaction (MSI) is crucial to comprehend how the catalyst support affects performance and whether this interaction can be exploited in order to design new catalysts with enhanced...

Resolving the Effect of Oxygen Vacancies on Co Nanostructures Using Soft XAS/X-PEEM

“…Subsequently, the sample was loaded into the X-PEEM apparatus via a preparation chamber that allows controlled gas dosing and heat treatment of the sample. 23 The X-PEEM images ( Figures 1 a and S4a–d ) contain spots with different brightness and diameters, reflecting the differences in the size of the NPs. The absolute size of the Co NPs was confirmed by high-resolution SEM ( Figures 1 b and S5 ), revealing the particles to be ∼10 times smaller than the size shown in the X-PEEM images ( Figure S4a–f ).…”

“…We attribute this disparity in Co/Ti-2 to the strong bonding interactions at the edge of Co NPs with the TiO 2 surface. 23 This also leads to differences in the degree of reduction of the centers of the NPs with those in region Co/Ti-1 being fully reduced for NPs < 15 nm (see Table 1 ), whereas in the region Co/Ti-2 only < 40% cobalt reduction is observed (see Table S1 ). The larger NPs in both samples are reduced to the lowest extent, particularly those in sample Co/Ti-2 present so much unreduced cobalt attributable to the high diffusion activation barrier.…”

“…At this point, we hypothesize that partial reduction of Co NPs has more to do with the properties of TiO 2 rather than the measurement performed on the sample. Subsequently, the sample was loaded into the X-PEEM apparatus via a preparation chamber that allows controlled gas dosing and heat treatment of the sample . The X-PEEM images (Figures a and S4a–d) contain spots with different brightness and diameters, reflecting the differences in the size of the NPs.…”

“… 9 , 21 This is further complicated by the tendency of NPs to agglomerate or else to become encapsulated by reduced TiO 2-x , 22 while recent reports have also shown Co NPs tend to spread on TiO 2 surfaces. 23 Consequently, alternative synthetic approaches need to be developed so as to enable facile Co NP reduction avoiding the well-documented downsides of the current preparation methods.…”

“…They are perhaps best known as catalysts for FTS, a widely applied method for the production of liquid transportation fuels and high-value chemicals, and are typically characterized by higher activity, higher chain-growth probability, and lower water gas shift activity than iron-based FTS catalysts . It has generally been shown that metallic Co NPs are the active phase on common supports such as TiO 2 , SiO 2, and Al 2 O 3 ; , cobalt oxide is typically present initially as Co 3 O 4 , which is then reduced to CoO and eventually Co metal before being used in the reaction. , The first step of Co 3 O 4 to CoO is comparatively easy to effect, while the second step of CoO to Co 0 is more difficult owing to the interaction between the metal and the support. , This is further complicated by the tendency of NPs to agglomerate or else to become encapsulated by reduced TiO 2‑x , while recent reports have also shown Co NPs tend to spread on TiO 2 surfaces . Consequently, alternative synthetic approaches need to be developed so as to enable facile Co NP reduction avoiding the well-documented downsides of the current preparation methods.…”