Effects of alkali adatoms on CO and H₂S adsorptions on the Fe(100) Surface: A density functional theory study

An alkali-added Fe catalyst is commonly used in the Fischer-Tropsch synthesis for fuel production from a mixture of CO and H₂ gases. The feed gas, however, also contains H₂S gas, which can shorten the activity life of the Fe catalyst. In this study, we have investigated how sodium and potassium affect the adsorption properties of CO and H₂S molecules adsorbed on the Fe(100) surface by using a density functional theory approach. It has been found that the presence of Na and K adatoms on the Fe(100) surface promotes the adsorption of the CO molecule and hinders the adsorption of the H₂S molecule, and in particular, the K adatom has been found to exert the largest variation effect on the adsorption energies. Through the examinations of local density of states and Bader charge analysis, we have shown that the electrostatic interactions between the alkali adatoms and the molecules are mainly responsible for such promotion and poison effects.