Carbon Formation Mechanism of C2H2 in Ni-Based Catalysts Revealed by in Situ Electron Microscopy and Molecular Dynamics Simulations

Understanding the carbon formation mechanism is critical for designing catalysts in various applications. Here, we report the observation of the carbon formation mechanism on Ni-based catalysts by environmental transmission electron microscopy (ETEM) over a wide temperature range in combination with molecular dynamics simulations and density functional theory calculations. In situ TEM observation performed in a C2H2/H-2 atmosphere provides real-time evidence that Ni3C is an intermediate phase that decomposes to graphitic carbon and metallic Ni, leading to carbon formation. Mechanisms of acetylene decomposition and evolution of carbon atom configuration are revealed by molecular dynamics simulations, which corroborate the experimental results. The modification of MgO on NiO can effectively decrease the formation of graphitic layers and thus enhance the catalytic performance of NiO. This finding may provide an insight into the origin of the carbon deposition and aid in developing effective approaches to mitigate it.