Читать книгу Heterogeneous Catalysts - Группа авторов - Страница 56

Carbons doped with heteroatoms (e.g. N, B, P, S) have the ability to coordinate transition‐metal atoms and thereby stabilizing them as single‐site catalyst. To prepare single‐atom sites, loading of metal deposits on the heteroatom‐doped carbon substrate can be carried out using traditional wet impregnation, followed by acid leaching to remove nanoparticles and noncoordinated metal atoms. This leaves behind the strongly bound single metal atoms, each coordinated by the surrounding heteroatom dopants. In particular, the strong interaction between N‐dopant and metals has been verified theoretically and experimentally using techniques X‐ray photoelectron spectroscopy (XPS), near edge X‐ray absorption fine structure (NEXAFS) [43], and transmission electron microscopy (TEM)–electron energy loss spectroscopy (EELS) [44]. The interaction is enabled by the delocalized free electrons of N on carbon. Their origins in turn can be explained by the electron back‐donation, where the σ‐type electron from the filled orbital of the N atom is donated to the empty orbital of the metal atom, leading to a π back‐donation from filled metal atomic orbital to the antibonding orbital of the N atom.