Elucidating the Stability and Reactivity of Surface Intermediates on Single-Atom Alloy Catalysts

Doping isolated single atoms of a platinum-group metal into the surface of a noble-metal host is sufficient to dramatically improve the activity of the unreactive host yet also facilitates the retention of the hosts high reaction selectivity in numerous catalytic reactions. The atomically dispersed highly active sites in these single-atom alloy (SAA) materials are capable of performing facile bond activations allowing for the uptake of species onto the surface and the subsequent spillover of adspecies onto the noble host material, where selective catalysis can be performed. For example, SAAs have been shown to activate C-H bonds at low temperatures without coke formation, as well as selectively hydrogenate unsaturated hydrocarbons with excellent activity. However, to date, only a small subset of SAAs has been synthesized experimentally and it is unclear which metallic combinations may best catalyze which chemical reactions. To shed light on this issue, we have performed a widespread screening study using density functional theory to elucidate the fundamental adsorptive and catalytic properties of 12 SAAs (Ni-, Pd-, Pt-, and Rh-doped Cu(111), Ag(111), and Au(111)). We considered the interaction of these SAAs with a variety of adsorbates often found in catalysis and computed reaction mechanisms for the activation of several catalytically relevant species (H-2, CH4, NH3, CH3OH, and CO2) by SAAs. Finally, we discuss the applicability of thermochemical linear scaling and the Bronsted-Evans-Polanyi relationship to SAA systems, demonstrating that SAAs combine weak binding with low activation energies to give enhanced catalytic behavior over their monometallic counterparts. This work will ultimately facilitate the discovery and development of SAAs, serving as a guide to experimentalists and theoreticians alike.