Fig. 3. Structural evolution and schematic diagram for the formation of core–shell FexCy particles. (a–d) TEM images of the fresh 10Fe/hNCNC-3 (a) and the spent 10Fe/hNCNC-3 undergoing 5, 10 and 60 h FTO reaction (b–d), respectively. (e–h) Typical high-resolution TEM images of the spent catalyst. The lattice spacings can be assigned to χ-Fe5C2, Fe7C3 and θ-Fe3C, corresponding to JCPDS no.: 089-8968, 075-1499 and 089-7271. (i) Illustration of the formation process of core–shell FexCy particles.
