Adsorption of CO, H2, H2O, and CO2 on Fe-, Co-, Ni-, Cu-, Pd-, and Pt-Doped Mo2C(101) Surfaces

To understand the mutual interaction and synergistic effect of transition metals and supports in heterogeneous catalysis, the less coordinated and more active surface MoA atoms were substituted with Fe, Co, Ni, Cu, Pd, and Pt doping atoms for investigating the adsorption of CO, H2, H2O, and CO2 as well as OH, H, and O. Metal loading affects the surface electronic structure. On these surfaces, Fe, Co, Ni, Cu, and Pd doping atoms are positively charged, indicating electron transfer from the metal to the surface, while Pt doping atoms are slightly negatively charged, revealing electron transfer from the surface to the metal. On the pure surfaces and surfaces doped with four metal atoms (4M, 25%), surface MoA atoms are most preferred adsorption sites. By replacing all surface MoA atoms with eight doping atoms (8M, 50%), the more coordinated and less active surface MoB atoms become active. Not only surface metal atoms but also surface carbon atoms are active for the adsorption of surface species. Depending on doping metals, the adsorption of surface species can become slightly more or less exothermic. Exploring the dissociative adsorption of H2O and CO2 reveals metal- and loading-dependent potential energy surfaces. Full H2O dissociative adsorption is favored thermodynamically on the 4M-doped surfaces and more exothermic than on the pure surface while doping metal-dependent on the 8M-doped surfaces. CO2 dissociative adsorption is thermodynamically favored on the 4M-doped surfaces, while it becomes endothermic on the 8M-doped surfaces, which prefer either molecular adsorption or equilibrium between molecular and dissociative adsorption. Comparing the adsorption of CO, OH, O, and H on the pure and doped Mo2C(101) surfaces as well as the corresponding metallic low-index M(hkl) surfaces reveals their similarity and difference. These results provide a basis for studying the mechanisms of reactions involving these surface species.