Surface speciation and alkane oxidation with highly dispersed Fe(III) sites on silica

► Impregnation of SiO2 with aqueous FeEDTA gives highly dispersed Fe3+. ► Isolated Fe3+ and 1-electron reduction shown by TPR, XPS, UV-vis. ► Na+ or NH4+ counterions control surface speciation. ► Na+: 'single-site' with 630 °C reduction and TOF0 ∼9 ks−1 in adamantane oxidation. ► NH4+: minority, reducible species shows similar TOF0 as isolated sites.