DFT investigations into surface stability and morphology of δ-MoC catalyst

The structures and stabilities of seven face-centered-cubic δ-MoC surfaces have been systematically investigated on the basis of periodic density functional theory computations of surface energies. The effects of carburization conditions in surface stability as well as catalyst morphology have also been researched by ab initio atomistic thermodynamics method. It has been found that with the increase of the carbon chemical potential (μ_C), the most stable surface changes from the carbon deficit metallic (311)-Mo termination to mixed Mo/C termination of (100) surface, and eventually to carbon rich (311)-C termination. It has also been found that δ-MoC catalyst has different morphologies at different carburization environments, i.e., only (311) surface is exposed on the nanoparticle at CH₄/H₂ gas mixture; (100) and (210) surfaces are exposed at μ_C comparable with graphite bulk energy; while (100), (210), and (311) surfaces are exposed at CO/CO₂ gas mixture. Our simulations provide the first understanding into the surface stability and morphology of this promising heterogeneous δ-MoC catalyst. In addition, the simulations facilitate a deeper understanding of the relationship between catalyst surface structure and experimental preparation conditions, which eventually provides the insights into the different catalytic properties of Mo carbide catalysts synthesized from different methods and procedures.