Impact of Carbonyl Formation on Cobalt Ripening over Titania Surface

Abstract

We present density functional theory calculations of the adsorption and migration energies of different cobalt moieties on the anatase (101) surface. Surface diffusion of active metal sites is a crucial step in the ripening mechanism, one of the primary causes for the loss of active surface area of cobalt Fischer–Tropsch catalyst. Our main objective is to clarify the impact of gas-phase molecules on the transport properties of surface-adsorbed cobalt. Notably, cobalt carbonyl species have the largest effect on the energetics of adsorption and surface diffusion. Water molecules physisorbed to the (101) surface have a negligible impact on the adsorption and diffusion of cobalt ions. The formation of Co(CO)3 is favorable under realistic reactor conditions and drastically decreases the surface binding energy, making transport via gas phase an alternative viable pathway for cobalt mobility.