Since Au turned out to be an active catalyst for CO oxidation at low temperatures, CO adsorption on various Au surfaces has been in the scope of numerous surface science studies. Interestingly, supported particles as well as stepped and rough single-crystal surfaces exhibit very similar adsorption behavior. To elucidate the origin of these similarities, we have performed temperature-programmed desorption and infrared absorption spectroscopy for a whole range of Au surfaces from nanoparticles grown on HOPG to Au(111) surfaces roughened by argon ion bombardment. In line with previous results, we have observed two desorption states at ∼130-145 and ∼170-185 K, respectively, and one infrared peak at around 2120 cm -1 in all cases. In addition to the experiments, we have carried out theoretical studies of CO adsorption on Au(332). The calculations show that CO desorption states above 100 K may be located at step-edges but not on terrace sites. Reducing the coordination of Au atoms further leads to successively higher binding energies with an unchanged anharmonic frequency. Therefore, we conclude that both desorption peaks belong to CO on low-coordinated Au atoms at steps and kinks. For the sputtered Au(111) surface, scanning tunneling microscopy reveals a rough pit-and-mound morphology with a large number of such sites. In annealing experiments we observe that the loss of these sites coincides with the loss of CO adsorption capacity, corroborating our conclusions.

Understanding the role of surface chemistry in the stability of nanostructured noble-metal materials is important for many technological applications but experimentally difficult to access and thus little understood. To develop a fundamental understanding of the effect of surface chemistry on both the formation and stabilization of self-organized gold nanostructures, we performed a series of controlled-environment annealing experiments on nanoporous gold (np-Au) and ion-bombarded Au(111) single-crystal surfaces. The annealing experiments on np-Au in ambient ozone were carried out to study the effect of adsorbed oxygen under dynamic conditions, whereas the ion-bombarded Au single-crystal surfaces were used as a model system to obtain atomic-scale information. Our results show that adsorbed oxygen stabilizes nanoscale gold structures at low temperatures whereas oxygen-induced mobilization of Au surface atoms seems to accelerate the coarsening under dynamic equilibrium conditions at higher temperatures.

Low‐coordinated gold atoms play a decisive role in the catalytic cycle of low‐temperature CO oxidation or the selective oxidation of olefins. A comparative study of argon and oxygen ion‐bombarded Au(111) surfaces (see microstructure images) reveals a threefold role of adsorbed oxygen: structure formation, stabilization of low‐coordinated gold atoms, and transfer during oxidation reactions.

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Gold with a nanoporous sponge-like morphology, generated by leaching of AuAg alloys is presented as a new unsupported material system for catalytic applications. The role of residual silver for catalytic activity towards CO oxidation in the temperature range from −20 to 50°C has been investigated by comparison with Au and Au/Ag zeolite catalysts. As revealed by a systematic variation of the silver content in the zeolite catalysts, bimetallic systems exhibit a significantly higher activity than pure gold, probably due to activation/dissociation of molecular oxygen by silver. By STEM tomography we can unambiguously prove that at least some of the particles form inside the zeolite lattice