Structural characterization by XAFS spectroscopy of non-porphyrin nickel in Liaohe vacuum residue

The local chemical structure of non-porphyrin Ni in Liaohe vacuum residue was investigated by X-ray absorption fine structure (XAFS) spectroscopy. Although the concentration of non-porphyrin Ni in the sample is very low, an available XAFS data was obtained by fluorescence mode. The X-ray absorption near edge structure (XANES) spectrum of the non-porphyrin Ni is similar to that in Ni (U) tetraphenylporphyrin, indicating the same Ni local structure. The extended X-ray absorption fine structure (EXAFS) result shows that the first coordination shells of Ni in the two samples are nearly identical, that is, non-porphyrin Ni also exists in a square-planar coordination of four N and the Ni-N distance is 0.192 nm.