A new model explaining carbon filament growth on nickel, iron, and NiCu alloy catalysts

Abstract

Kinetic results for carbon deposition and gasification on supported nickel catalysts, in terms of rates as functions of gas composition, and a new estimate of the energy of formation of carbon filaments are presented. On the basis of these results together with results from previous studies of carbon filament growth on supported nickel, iron, and nickel-copper catalysts, as well as studies of carbon atom interactions with nickel single-crystal surfaces, a new model explaining carbon filament growth on supported transition metal catalysts is suggested. The new model is compared with the “classical” model and with a recently proposed model based on the assumption that an unstable bulk carbide governs the filament growth. In contrast to previous models, the new model explains all observations and agrees with available thermodynamic equilibrium data. It also provides in a natural way a driving force for the migration of carbon atoms through the catalyst particle.