Hagg carbide surfaces induced Pt morphological changes: a theoretical insight

Comprehensive spin-polarized density functional theory (DFT) combined with ab initio molecular dynamic (AIMD) simulations have been performed to explore the structures, energies, and diffusion behavior of platinum on Fe5C2 surfaces with importance in Fischer-Tropsch (F-T) catalysis. The results indicate that the morphology of the Pt promoter on Hagg carbide highly depends on the surface structure of the Fe5C2. The Fe5C2(111) surface shows a stronger Pt affinity than the Fe5C2(100) surface, while the Fe5C2(100) surface has stronger Pt-n aggregation ability. Under the realistic iron-based F-T reaction conditions, the adsorbed Pt atoms can diffuse easily, and tend to aggregate following the line-band-layer mode on Fe5C2(100). While on the Fe5C2(111) surface, the adsorbed Pt atoms prefer sitting on the most stable sites, and form dispersed structures rather than aggregated structures until the coverage of Pt is above 2/7 (the surface atom ratio of Pt to Fe). In addition, the three-dimensional structures are not favored on both surfaces because of the stronger Fe-Pt interaction over the Pt-Pt bonding. The adsorbed Pt atoms possess negative charges and the stronger electron transfer is observed on the Fe5C2(100) surface, especially at the low coverage.