The presence of carbon on and in catalytically active metal particles can alter the particle's catalytic activity. Carbon dissolution and transport kinetics have also been implicated in the epitaxial growth of graphene on Ni crystals. We use a novel molecular beam reflectivity method to elucidate the diffusion kinetics of carbon on and into a flat Ni(111) and a lightly stepped Ni(997) surface. Real-time reactivity measurements of methane dissociation on the surface provide a readout of surface carbon coverage and reactivitiy. We observe clear evidence for islanding of C on the Ni(111) surface at intermediate temperatures, and the onset of diffusion from the surface into sub-surface sites at temperatures of 700K and above. Studies on the Ni(997) surface show similar trends, but the onset of C dissolution into sub-surface sites occurs at a lower surface temperature. Our ability to monitor carbon dissolution kinetics over a wide range of timescales and surface temperatures allows us to quantify the diffusion barrier for transport of surface-bound C into the subsurface region and gain insight into the role of steps in promoting carbon transport.

Kinetics of carbon transport and dissolution on Ni(111) and Ni(997) and impacts on methane activation.

ACS Spring Meeting 2021

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