Coking mechanism and promoter design for Ni-based catalysts: A first principles study

Abstract

Based on a first principles study of the interaction of carbon with Ni(111), a new way is proposed to improve the coking resistance of Ni-based catalysts. Three forms of chemisorbed carbon - on-surface carbon atoms, bulk nickel carbide and graphene - are distinguished and their relative stability is studied. At low coverages, on-surface carbon atoms will diffuse to the Ni bulk until saturation at a C:Ni mole fraction of about 1:2. The formation of the carbide will affect the catalytic properties of Ni and might lead to catalyst deactivation. When the on-surface carbon can accumulate to high coverages, formation of a graphene overlayer becomes preferred, leading to surface blocking and catalyst deactivation. Boron was found to be a potential promoter to prevent coking of Ni-based catalysts by effectively blocking the diffusion of carbon into the Ni bulk. © World Scientific Publishing Company.