Carbon Nanosphere-Encapsulated Fe Core–Shell Structures for Catalytic CO2 Hydrogenation

We synthesized a unique carbon nanosphere (CNS)-encapsulated Fe core–shell catalyst (CNS–Fe) for CO2 hydrogenation. The synthesized CNS–Fe catalyst exhibited a core–shell structure with a core of ca. 40 nm containing iron species and a shell thickness of ca. 10 nm composed of mainly graphitic carbon. X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis were used to characterize the fresh and spent CNS–Fe catalysts and reveal a mixture of Fe3O4, metallic Fe, and Fe5C2 in the core and graphitic carbon as the shell with defect sites. Hydrogen temperature-programmed reduction, X-ray absorption near-edge structure, and extended X-ray absorption fine structure for the fresh CNS–Fe confirmed the composition of the iron species encapsulated in the CNS. The catalytic performance of CNS–Fe was investigated at ambient pressure for CO2 hydrogenation with hydrocarbons (CH4, C2–C4=, C2–C40), and CO was observed as the main product.