Well-defined and perfectly dispersed [(square SiO)Au(1)] surface species supported on silica have been obtained via surface organometallic chemistry and transformed upon mild reduction (H(2), 300 degrees C) into small (1.8 +/- 0.6 nm) Au particles supported on silica passivated with SiMe(3) functionalities. improved performance in liquid-phase aerobic epoxidation has been achieved, and the intrinsic activity of gold in oxidation is revealed.