We also see an increase in the lowest ethylene C-H activation barrier for Pt 4 C 2 relative to Pt 4 , indicating an increase in selectivity (Fig. ). This agrees with literature; 17 even the inclusion of a small amount of carbon on Pt, either in bulk, or larger more bulk-like NPs will dramatically reduce the activity towards ethane dehydrogenation, while improving selectivity towards ethylene. The charge distributions in Figure ), calculated using QTAIM, reveal details of the mechanism of electronic deactivation. The carbon atoms are negatively charged, having drawn electron density away from the platinum atoms, as expected from Pauling electronegativity values. A similar charge-transfer effect has been observed experimentally in S-doped Pt catalysts by XPS and CO stretching frequencies. With this in mind, we next investigate the efect of Ge doping on catalyst stability and selectivity. Returning to the supported cluster model, Figure and the integrated crystal orbital bond index (ICOBI) values for the C-C atomic pair. COHP shows the bonding character of electronic states between specific pairs of atoms or orbitals, where bonding states appear to the right of the vertical axis (note that the horizontal axis plots -COHP so that positive values denote bonding orbitals). The PDOS peaks around the Fermi level, as discussed above, are present in the bonding channel on the COHP plots, indicating that these states have strong C-C bonding character. ICOBI is a bond order for pairs of atoms in solids, 37 so the increase in C-C ICOBI from 1.20 to 1.55 on addition of Ge is further evidence for a strengthened C-C bond. We can therefore conclude that the Ge dopant donates electrons to C, so Pt remains electron-rich and reactive, while remaining selective. The donated electrons occupy a π C-C bonding orbital, so Ge doping strengthens C-C bonding as indicated by the gas phase models.