2 research outputs found
On-Surface Hydrogen-Induced Covalent Coupling of Polycyclic Aromatic Hydrocarbons via a Superhydrogenated Intermediate
The activation and subsequent covalent coupling of polycyclic aromatic
hydrocarbons (PAHs) are of great interest in fields like chemistry, energy,
biology, or health, among others. However, this is not a trivial process. So
far, it is based on the use of catalysts that drive and increase the efficiency
of the reaction. Here, we report on an unprecedented method in which the
dehydrogenation and covalent coupling is thermally activated in the presence of
atomic hydrogen and a surface. This mechanism, which requires of the
superhydrogenation of the PAHs, has been characterized by high-resolution
scanning tunnelling microscopy (STM) and rationalized by density functional
theory (DFT) calculations. This work opens a door toward the formation of
covalent, PAH-based, macromolecular nanostructures on low-reactive surfaces,
thus facilitating its applicability.Comment: This manuscript version is made available under the CC-BY-NC-ND 4.0
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Catalytic Oxidation of Carbon Monoxide on a Curved Pd Crystal: Spatial Variation of Active and Poisoning Phases in Stationary Conditions
Understanding
nanoparticle catalysis requires novel approaches
in which adjoining crystal orientations can be studied under the same
reactive conditions. Here we use a curved palladium crystal and near-ambient
pressure X-ray photoemission spectroscopy to characterize chemical
species during the catalytic oxidation of CO in a whole set of surfaces
vicinal to the (111) direction simultaneously. By stabilizing the
reaction at fixed temperatures around the ignition point, we observe
a strong variation of the catalytic activity across the curved surface.
Such spatial modulation of the reaction stage is straightforwardly
mapped through the photoemission signal from active oxygen species
and poisoning CO, which are shown to coexist in a transient regime
that depends on the vicinal angle. Line-shape analysis and direct
comparison with ultrahigh vacuum experiments help identifying and
quantifying all such surface species, allowing us to reveal the presence
of surface oxides during reaction ignition and cooling-off