Theoretical Calculations on the Stability of Carbide Layers at Transition Metal Surfaces

Abstract

Local density of states (LDOS) calculations have been performed on bulk and surface carbides of iron, nickel and copper. Foccussing on the splitting of the carbon p-orbitals and the degree of filling of the anti-bonding p-orbital, we conclude that the stability of the bulk carbides decreases from iron to nickel to copper, in agreement with experimentally known fact. This trend is also observed in the surface carbides, and it is concluded that a carbide layer is unstable on copper surfaces, with respect to graphite. The implications of these results for the mechanism and selectivity in Fischer-Tropsch synthesis on these metals is discussed. Using ideas from Effective Medium Theory, we have also examined the behaviour of various carbon layers on a Ni(111) surface, with a view to examining the mechanism for carbide to graphite transformation. Some preliminary results are presented here.