Towards understanding the role of carbon atoms on transition metal surfaces: Implications for catalysis

Carbon moieties, in a low coverage regime being reduced to C adatoms, are a rock-in-the-shoe for heterogeneously catalyzed processes involving carbon-containing species. Their presence affects the performance of Transition Metal (TM) based industrial catalysts, often resulting in poisoning. Recent studies on the C adatom thermodynamic stability revealed that both surface and subsurface C atoms may coexist, indicating additional poisoning mechanisms, yet also new catalytic promoting mechanisms. The present work provides a systematic study of the potential dynamic relevance of such subsurface C atoms in the most stable (111) surface of all fcc TMs at low C coverages. This relies on evaluating the composition at thermodynamic equilibrium and the time scale of the different involved processes by means of Density Functional Theory (DFT) and kinetic Monte Carlo (kMC) simulations, respectively. These DFT and kMC simulations highlight the relevant role of subsurface C atoms for Ag and Pd, and a fast C mobility for Au and Pt, which might be important factors contributing to poisoning or opening new reactive path mechanisms, especially relevant at high temperature working conditions.