Effect of platinum promoters on the removal of O from the surface of cobalt catalysts: A DFT study

Cobalt is one of the commonly used catalysts in Fischer-Tropsch Synthesis (FTS). Small amounts of Pt are often added to cobalt to prevent deactivation and improve activity [1]. Removal of oxygen from the cobalt surface is one of the final steps in FT'S mechanism. We investigate the role of the surface platinum promoter in the removal of oxygen from the cobalt surface using density functional theory (DFT) calculations. The activation barriers and transition states on both flat and stepped Co(0001) surfaces for the removal of oxygen from the cobalt surface with and without the presence of platinum were calculated using the Climbing Image Nudged Elastic Band (CI-NEB) method [2-4]. When Pt atoms are present on the surface, the activation barrier for the removal of O is reduced when compared to that on an un-promoted cobalt catalyst. The reduced barrier is attributed to the change in the electronic structure of the catalyst surface as evidenced from a shift in the d-band center and also a transfer of electrons from Co to Pt in agreement with an experimental study [5]. A micro-kinetic analysis shows that the turnover frequency (TOF) of oxygen removal for promoted Co surface increases when compared to that on un-promoted Co surface, with potential for further improvement The results support the conjecture that surface Pt atoms helps reduce deactivation of cobalt catalyst by promoting oxygen removal from the surface. (C) 2011 Elsevier B.V. All rights reserved.