A theoretical study of CO adsorption on FeCo(100) and the effect of alloying

FeCo catalysts are modeled for optimizing the Fischer-Tropsch synthesis process since they can be tuned to enhance CO activity and resist poisoning. The electronic properties associated with CO adsorption are studied using plane-wave density functional theory (DFT). The range of computed adsorption energies from this work falls between the CO adsorption energies on pure Fe and Co surfaces. It was found that CO prefers to adsorb on the top site of the Co surface of FeCo alloys, whereas CO has stronger adsorption on pure Fe rather than pure Co surface. The trend in adsorption energy is top-Co > hollow-Fe > top-Fe > hollow-Co > bridge-Co > bridge-Fe. This change in preferable metal for adsorption (i.e.. from Fe in a pure system to Co in the FeCo alloy surface in the current investigation) is due to the shift in the d-band center of the alloyed material. It implies that alloying Fe with Co changes the properties of the pure metal and ultimately affects the CO adsorption energy; however, the mechanism of adsorption remains similar and can be explained using the Nilsson-Pettersson model. Additional CO configurations consisting of hollow-site adsorption with a tilted geometry, was also investigated. The corresponding adsorption energy was found to be slightly higher than the adsorption energy when CO is adsorbed on the top-Co site. (C) 2011 Elsevier B.V. All rights reserved.