The reactivity of catalytic surfaces is often dominated by very reactive low-coordinated atoms such as step-edge sites. However, very little knowledge exists concerning the influence of step edges on the selectivity in reactions involving multiple reaction pathways. Such detailed information could be very valuable in rational design of new catalysts with improved selectivity. Here we show, from an interplay between scanning tunnelling microscopy experiments and density functional theory calculations, that the activation of ethylene on Ni(111) follows the trend of higher reactivity for decomposition at step edges as compared with the higher-coordinated terrace sites. The step-edge effect is considerably more pronounced for the C-C bond breaking than for the C-H bond breaking, and thus steps play an important role in the bond-breaking selectivity. Furthermore, we demonstrate how the number of reactive step sites can be controlled by blocking the steps with Ag. This approach to nanoscale design of catalysts is exploited in the synthesis of a new high-surface-area AgNi alloy catalyst, which is tested in hydrogenolysis experiments.

The primary route to hydrogen production from fossil fuels involves the water-gas shift (WGS) reaction, and an improvement in the efficiency of WGS catalysts could therefore lead to a major leap forward in the realization of hydrogen economy. On the basis of a combination of high-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations, we suggest the existence of a new thermodynamically stable Cu/Pt near-surface alloy (NSA). Temperature-programmed desorption and DFT reveal that this Cu/Pt NSA binds CO significantly more weakly than does Pt alone, thereby implying a considerable reduction in the potential for CO poisoning of the Cu/Pt NSA surface as compared to that of pure Pt. In addition, DFT calculations show that this Cu/Pt NSA is able to activate H2O easily, which is the rate-determining step for the WGS on several metal surfaces, and, at the same time, to bind the products of that reaction and formate intermediates rather weakly, thus avoiding possible poisoning of the catalyst surface. The Cu/Pt NSA is thus a promising candidate for an improved WGS catalyst.

High-pressure scanning tunneling microscopy was used to study the room-temperature adsorption of CO on a Pt(111) single-crystal surface in equilibrium with the gas phase. The coverage was found to vary continuously, and over the entire range from 10 -6 -760 Torr pressure-dependent moiré patterns were observed, characteristic of a hexagonal or nearly hexagonal CO overlayer. Two different pressure ranges can be distinguished: below 10 -2 Torr, the moiré lattice vector is oriented along a 30°high-symmetry direction of the substrate, corresponding to a pressure-dependent rotation of the CO overlayer with respect to the (1 × 1) Pt surface lattice, while above 10 -2 Torr, the CO layer angle is independent of the pressure. This behavior is analyzed in terms of the interplay of the repulsive CO-CO interaction potential and the substrate potential.

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The oxidized Ag(111) surface has been studied by a combination of experimental and theoretical methods, scanning tunneling microscopy, x-ray photoelectron spectroscopy, and density functional theory. A large variety of different surface structures is found, depending on the detailed preparation conditions. The observed structures fall into four classes: (a) individually chemisorbed atomic oxygen atoms, (b) three different oxygen overlayer structures, including the well-known p(4x4) phase, formed from the same Ag₆ and Ag₁₀ building blocks, (c) a c(4x8) structure not previously observed, and (d) at higher oxygen coverages structures characterized by stripes along the high-symmetry directions of the Ag(111) substrate. Our analysis provides a detailed explanation of the atomic-scale geometry of the Ag₆/Ag₁₀ building block structures and the c(4x8) and stripe structures are discussed in detail. The observation of many different and co-existing structures implies that the O/Ag(111) system is characterized by a significantly larger degree of complexity than previously anticipated, and this will impact our understanding of oxidation catalysis processes on Ag catalysts