Theoretical Investigation of Cobalt Cluster Size on Adsorption Kinetics in Fischer-Tropsch Synthesis

Abstract

In this study, the particles of cobalt with different sizes were simulated by Materials Studio software then the adsorption of H2, CO, and CH4 and its components (CH, CH2, CH3) as Fischer-Tropsch synthesis monomers were investigated using Density-functional theory. The results showed that the suitable sites for the adsorption of CO, H2 and monomers in Fischer-Tropsch synthesis are affected by the size of cobalt clusters. Increasing in the size of the cobalt cluster, the number of suitable sites for adsorption of the species decreases. In general, H2 adsorption energy decreases with increasing cobalt cluster size because larger clusters tend to have a less reactive surface due to increased coordination number and reduced surface charge density. On the other hand, CO adsorption energy tends to increase with cluster size because the larger clusters can accommodate the linear CO molecule more effectively due to their extended surface area. With considering the deformation of adsorbed species, Mulliken charge result, density of states and partial density of states, it could be stated that all species were chemically adsorbed on the surface of clusters, except CH4 that was adsorbed on Co-10 and Co-18 clusters is physically. Kinetic parameters for H2 and CO adsorption were calculated considering the change in cobalt cluster size.