Au Catalyzed Carbon Diffusion in Ni: A Case of Lattice Compatibility Stabilized Metastable Intermediates

Nickel is a crucial catalyst for its excellent performance in active carbon atom-related catalysis such as hydrocarbon steam reforming and 1D carbon nanostructures preparation. The carbon diffusion activity in Ni is of critical importance in understanding the catalytic behavior and thereby the performance optimization. However, the carbonization process is still vague because of the hardly identified intermediates. In this paper, the metastable intermediates of nickel carbonization process are successfully stabilized by taking advantage of the epitaxial growth to elevate the structure transformation energy barrier. X-ray diffraction, high-resolution transmission electron microscopy, and synchrotron X-ray absorption near edge structure data evidence the face-centered cubic (fcc)-NixC nature of the intermediates and thus an fcc-NixC-intermediated nickel carbonization process from fcc-Ni to hexagonal close-packed (hcp)-Ni3C is revealed, which is also confirmed by the Vienna ab initio simulation package calculation from the viewpoint of energy evolution. To the best of the knowledge, it is the first time to report the identification of the fcc-NixC. More importantly, the introduction of Au is found promoted the catalytic growth of graphitic carbon using either oleylamine or C2H4 as carbon resource. The Au@Ni-based hybrid catalysts exhibit lower reaction temperature and much higher carbon output than pure Ni.