Curved crystal surfaces enable the systematic and accurate comparison of physical and chemical processes for a full set of vicinal crystal planes, which are probed in the very same environment. Here, we examine the early stages of the CO chemisorption on vicinal Rh(111) surfaces using a curved Rh crystal that exposes a smoothly variable density of {100} (A-type) and {111} (B-type) steps. We readily identify and quantify step and terrace species by resolving their respective core-level lines using X-ray photoelectron spectroscopy at different locations on the curved surface. Uptake experiments show similar sticking probabilities at all surface planes, subtle asymmetries between A- and B-type steps, and significantly lower saturation coverage at densely stepped surfaces as compared to the (111) plane. The analysis of the C 1s intensity variation across the curved sample allows us to discuss the adsorption geometry around the step edge.

The catalytic oxidation of CO on transition metals, such as Pt, is commonly viewed as asharp transition from the CO-inhibited surface to the active metal, covered with O. However,w ef ind that minor amounts of Oa re present in the CO-poisoned layer that explain why,surprisingly,COdesorbs at stepped and flat Pt crystal planes at once,r egardless of the reaction conditions.Using near-ambient pressure X-ray photoemission and ac urved Pt(111) crystal we probe the chemical composition at surfaces with variable step density during the CO oxidation reaction. Analysis of Cand Ocore levels across the curved crystal reveals that, right before light-off,subsurface Ob uilds up within (111) terraces.T his is key to trigger the simultaneous ignition of the catalytic reaction at different Pt surfaces:aCO-Pt-O complex is formed that equals the CO chemisorption energy at terraces and steps,l eading to the abrupt desorption of poisoning CO from all crystal facets at the same temperature.

The state of the surface near-region during CO hydrogenation of Ni(111) and Ni(211) single crystal surfaces was investigated using various gas mixtures between 150 and 500 mbar, 200 and 325 °C, by operando X-ray photoelectron spectroscopy. We report how higher temperatures and hydrogen content correlate with a movement of CO away from the on-top configurations and toward multicoordinated sites of the nickel surface and how a nickel carbide is formed in the surface near region, particularly at high partial pressures of CO and lower temperatures. The presence of the carbide affects the CO bonding and was observed to be reduced during hydrogen-rich conditions and temperatures above 250 °C.

Steps at metal surfaces may influence energetics and kinetics of catalytic reactions in unexpected ways. Here, we report a significant reduction of the CO saturation coverage in Pd vicinal surfaces, which in turn is relevant for the light-off of the CO oxidation reaction. The study is based on a systematic investigation of CO adsorption on vicinal Pd(111) surfaces making use of a curved Pd crystal. A combined X-ray Photoelectron Spectroscopy and DFT analysis allows us to demonstrate that an entire row of atomic sites under Pd steps remains free of CO upon saturation at 300 K, leading to a step-density-dependent reduction of CO coverage that correlates with the observed decrease of the light-off temperature during CO oxidation in vicinal Pd surfaces.

Rotaxanes, formed by an axis through the cavity of a macrocycle, are promising systems for the construction of molecular machines. A very limited number of experimental techniques are available for mechanistic studies since only mechanical bonds are formed, being NMR one of the most widely used. The major inconvenience derived from NMR use is the time-scale for threading/dethreading processes lasting a few minutes in the case of faster processes. In the present manuscript, we report the application of a new kinetic methodology based on a displacement assay for cyclodextrin-based pseudorotaxane formation. By coupling a very fast (microseconds time-scale) binding/dissociation of nitrophenol to α-CD with a dicationic axle threading/dethreading process, we have been able to study kinetic processes taking place in the millisecond time-scale.

Curved crystals are a simple but powerful approach to bridge the gap between single crystal surfaces and nanoparticle catalysts, by allowing a rational assessment of the role of active step sites in gas-surface reactions. Using a curved Rh(111) crystal, here, we investigate the effect of A-type (square geometry) and B-type (triangular geometry) atomic packing of steps on the catalytic CO oxidation on Rh at millibar pressures. Imaging the crystal during reaction ignition with laser-induced CO2 fluorescence demonstrates a two-step process, where B-steps ignite at lower temperature than A-steps. Such fundamental dissimilarity is explained in ambient pressure X-ray photoemission (AP-XPS) experiments, which reveal partial CO desorption and oxygen buildup only at B-steps. AP-XPS also proves that A-B step asymmetries extend to the active stage: at A-steps, low-active O–Rh–O trilayers buildup immediately after ignition, while highly active chemisorbed O is the dominant species on B-type steps. We conclude that B-steps are more efficient than A-steps for the CO oxidation.

The catalytic oxidation of CO on transition metals, such as Pt, is commonly viewed as asharp transition from the CO-inhibited surface to the active metal, covered with O. However,w ef ind that minor amounts of Oa re present in the CO-poisoned layer that explain why,surprisingly,COdesorbs at stepped and flat Pt crystal planes at once,r egardless of the reaction conditions.Using near-ambient pressure X-ray photoemission and ac urved Pt(111) crystal we probe the chemical composition at surfaces with variable step density during the CO oxidation reaction. Analysis of Cand Ocore levels across the curved crystal reveals that, right before light-off,subsurface Ob uilds up within (111) terraces.T his is key to trigger the simultaneous ignition of the catalytic reaction at different Pt surfaces:aCO-Pt-O complex is formed that equals the CO chemisorption energy at terraces and steps,l eading to the abrupt desorption of poisoning CO from all crystal facets at the same temperature.

We combine PLIF and NAP-XPS to investigate the CO oxidation reaction at vicinal Pt(111) surfaces in the millibar regime, using a curved sample. We find that the catalytic activation of Pt occurs in all vicinal planes simultaneously,<br>irrespectively of the reaction parameters. The systematic analysis of chemical species across the entire curved surface provides the clues for this surprising behavior. As the surface CO concentration decreases when approaching ignition, minor amounts of oxygen build up at both steps and (111) terraces. First-principles theory indicates that the latter is forming a CO-Pt-O complex that binds CO molecules to terraces strongly, leveling its adsorption energy to that of low-coordinated steps, and explaining why CO abruptly desorbs at the same temperature along the di erent crystal facets that make up the curved Pt surface.