Subsurface Carbon - a General Feature of Noble Metals.

Carbon Cn moieties on late transition metals are historically regarded as poisoning agents for their use in heterogeneous catalysis. Recent experimental studies combining ab initio simulations showed the promoting catalytic role of subsurface C atoms in Pd surfaces, plus their existence was well established in Ni and Pt surfaces. Here we show, adjoining energetic and kinetic evidences obtained by accurate density functional simulations on surface and nanoparticle models, that such subsurface C species are a general issue to be considered even in coinage noble metal systems. Subsurface C is the most stable situation in densely packed (111) surfaces of Cu and Ag, with sinking barriers low enough to be overcome at catalytic working temperatures. Low-coordinated sites at nanoparticles edges and corners further stabilize them, even in gold, with negligible subsurface sinking barriers. The malleability of low-coordinated sites appears to be the key aspect in the subsurface C accommodation. The incorporation of C species decreases the electron density of the surrounding metal atoms, thus affecting their chemical and catalytic activity. These results broaden the subsurface C chemistry, so as to be considered a general aspect to be regarded in future studies on heterogeneously catalysed processes by late transition metal systems.