Activation of Single Atom Alloys towards Alkyl C–H Bond: A Theoretical Study

Single atom alloys (SAAs), composed of active metal dopants atomically dispersed on the Cu, Ag, or Au host metals, have recently become a “rising star” in single atom catalysis research. SAAs usually display unique catalytic behavior, mainly due to the anomalous electronic structure of isolated active sites, distinguishing from that of the parent metals. As the consequence, there is lack of robust and reliable descriptor of catalytic properties of SAAs. In this work, we present a systematically theoretical study on the first C–H bond activation of methane, propane and ethylbenzene over 15 SAAs comprising of Rh, Ir, Ni, Pd, and Pt doping Cu(111), Ag(111), and Au(111) surfaces. Our DFT calculations demonstrate that not only the d-band centers but also the H atom adsorption energies can not correlate well with the activation barriers of alkyl C–H bond, while enhanced performance is achieved when using the reaction energy as a descriptor. We find that there exists orbital interaction similarity between C atom adsorption on top site and the transition states of C–H activation because both of them involve not only σ donation with d_z² orbital but also the π back-donation from d_xy/d_yz orbital(s). As a consequence, the C adsorption energies and C–H bond activation energies are very strongly correlated (R²>0.9), not only for methane but also for propane and ethylbenzene.