Insights into Single-Atom Catalysts on Oxygen Functionalized Carbon Nanotubes

The structure of heterogeneous catalysts should be understood at the atomic level because the metal centers supported on different defects on support surfaces have completely different microenvironments and reactive behaviors. However, due to the lack of a fundamental understanding of the surface properties of supports, like carbon materials, distinguishing properties of different metal sites on the supports has always been a challenge. In this study, we employed vanadium and platinum catalysts supported on functionalized carbon nanotubes to demonstrate that metal catalysts supported on carbon materials exhibit different properties depending on the type of surface functional groups. The oxygen functional groups on carbon form covalent bonds with the vanadium (or platinum) precursor, leading to atomically dispersed metal oxide (or metal) deposition. Comprehensive investigations were performed to demonstrate the differences in the interactions between the metal species and each type of functional group. The results revealed that vanadium species to carboxylic and anhydride groups agglomerated at lower temperatures than the species bonded to phenol groups. Moreover, the platinum species on different oxygen functional groups on the carbon nanotubes exhibited distinct catalytic activities in the reverse water-gas shift reaction. These results suggest that determining the surface chemistry of carbon materials used as supports is highly significant for developing carbon-based heterogeneous catalysts and understanding the related catalytic processes. Anchoring single-atom metal species on oxygen-functionalized carbon nanotubes via a straightforward method provides an ideal model system for investigating carbon surface chemistry and the catalytic properties of carbon-supported metal sites (C-O-M species).