  We report CO-induced lifting of the hexagonal surface reconstruction on Au
(001). Using in-situ surface x-ray scattering, we determined a
pressure-temperature phase diagram for the reconstruction and measured the
dynamical evolution of the surface structure in real time. Our observations
provide evidence that, under certain conditions, even macroscopic Au surfaces,
much larger than catalytic Au nanoparticles [M. Haruta, Catal. Today 36, 153
(1997)], can exhibit some of the reactive properties and surface transitions
observed in systems known to be catalytically active such as Pt (001).
