Adsorption of normal-alkanes on Fe(110), FeO(110), and Fe2O3(0001): Influence of iron oxide surfaces
A comparative analysis of adsorption of six normal-alkanes (CNH2N+2, N = 4, 6, 8, 10, 12, 16) on Fe(110), FeO(110), and Fe2O3(0001) was carried out using classical molecular dynamics (MD) simulation. A realistic model system for adsorbed alkanes was employed using the COMPASS force field (FF), while the appropriate relaxed surfaces and an effective interfacial potential were obtained from ab initio calculations. The results show that butane molecules orient randomly on Fe(110) and Fe2O3(0001) surfaces, but they preferentially orient in the (010) direction on FeO(110) at low temperature. Additionally, alkanes adsorb physically on Fe(110), FeO(110), and Fe2O3(0001), in the following decreasing order Fe(110) > FeO(110) > Fe2O3(0001). The adsorption energies per saturated carbon site decrease with an increase of molecular chain length, and this propensity is similar for different surface potentials. In contrast, the saturated carbon density is insensitive to the surface potentials and shows an increasing trend for short alkane chains, but it remains steady for longer chains.