Effect of carbon on the Ni catalyzed methane cracking reaction: A DFT study

Abstract

• Effect of carbon deposition on kinetic properties of methane dissociation is studied. • Existence of surface and subsurface C atoms destabilized CH x species adsorption. • CH x activation is hindered with the deposition of C on and in the Ni (1 1 1) surface. To understand the effects of carbon atoms on the Ni catalyzed methane cracking reactions, methane dissociation on clean, surface-carbon-covered, and subsurface-carbon-accumulated Ni(1 1 1) surfaces were investigated using density functional theory (DFT). The results show that the existence of surface and subsurface C atoms destabilized the adsorption of the surface hydrocarbon species when compared to the clean Ni(1 1 1) surface. The projected density state (PDOS) analysis shows that the deposition of C atoms on and into the Ni surface modified the electronic structure of the Ni surface, and thus reduced the catalytic activity of the bonded Ni atoms. Moreover, it was found that the presence carbon atoms increase the CH x ( x = 4–1) species activation barriers especially on the surface carbon covered (1/4 ML) Ni(1 1 1) surface, where CH x ( x = 4–1) species encounter highest energy barrier for dissociation due to the electronic deactivation induced by C Ni bonding and the strong repulsive carbon CH x interaction. The calculations also show that CH x dissociation barriers are not affected by its neighboring C atom at low surface carbon coverage (1/9 ML). This work can be used to estimate more realistic kinetic parameters for this system.