| 1. |
- Winkler, P., et al.
(författare)
-
Coexisting multi-states in catalytic hydrogen oxidation on rhodium
- 2021
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- Catalytic hydrogen oxidation on a polycrystalline rhodium foil used as a surface structure library is studied by scanning photoelectron microscopy (SPEM) in the 10−6 mbar pressure range, yielding spatially resolved X-ray photoemission spectroscopy (XPS) measurements. Here we report an observation of a previously unknown coexistence of four different states on adjacent differently oriented domains of the same Rh sample at the exactly same conditions. A catalytically active steady state, a catalytically inactive steady state and multifrequential oscillating states are simultaneously observed. Our results thus demonstrate the general possibility of multi-states in a catalytic reaction. This highly unusual behaviour is explained on the basis of peculiarities of the formation and depletion of subsurface oxygen on differently structured Rh surfaces. The experimental findings are supported by mean-field micro-kinetic modelling. The present observations raise the interdisciplinary question of how self-organising dynamic processes in a heterogeneous system are influenced by the permeability of the borders confining the adjacent regions.
|
|
| 2. |
- Datler, M., et al.
(författare)
-
Visualizing catalyst heterogeneity by a multifrequencial oscillating reaction
- 2018
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- It is well documented that different surface structures of catalytically active metals may exhibit different catalytic properties. This is typically examined by comparing the catalytic activities and/or selectivities of various well-defined smooth and stepped/kinked single crystal surfaces. Here we report the direct observation of the heterogeneity of active polycrystalline surfaces under reaction conditions, which is manifested by multifrequential oscillations during hydrogen oxidation over rhodium, imaged in situ by photoemission electron microscopy. Each specific surface structure, i.e. the crystallographically different µm-sized domains of rhodium, exhibits an individual spiral pattern and oscillation frequency, despite the global diffusional coupling of the surface reaction. This reaction behavior is attributed to the ability of stepped surfaces of high-Miller-index domains to facilitate the formation of subsurface oxygen, serving as feedback mechanism of the observed oscillations. The current experimental findings, backed by microkinetic modeling, may open an alternative approach towards addressing the structure-sensitivity of heterogeneous surfaces.
|
|
| 3. |
- Suchorski, Y., et al.
(författare)
-
Resolving multifrequential oscillations and nanoscale interfacet communication in single-particle catalysis
- 2021
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 372:6548, s. 1314-1318
-
Tidskriftsartikel (refereegranskat)abstract
- In heterogeneous catalysis research, the reactivity of individual nanofacets of single particles is typically not resolved. We applied in situ field electron microscopy to the apex of a curved rhodium crystal (radius of 650 nanometers), providing high spatial (∼2 nanometers) and time resolution (∼2 milliseconds) of oscillatory catalytic hydrogen oxidation, to image adsorbed species and reaction fronts on the individual facets. Using ionized water as the imaging species, the active sites were directly imaged with field ion microscopy. The catalytic behavior of differently structured nanofacets and the extent of coupling between them were monitored individually. We observed limited interfacet coupling, entrainment, frequency locking, and reconstruction-induced collapse of spatial coupling. The experimental results are backed up by microkinetic modeling of time-dependent oxygen species coverages and oscillation frequencies.
|
|
| 4. |
- Sternig, A., et al.
(författare)
-
Phase Separation at the Nanoscale: Structural Properties of BaO Segregates on MgO-Based Nanoparticles
- 2011
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:32, s. 15853-15861
-
Tidskriftsartikel (refereegranskat)abstract
- Composite BaO/MgO nanoparticles have been prepared by chemical vapor synthesis and subsequent annealing in controlled gas atmospheres. High resolution transmission electron microscopy and X-ray diffraction reveal that a part of the obtained nanoparticles can be characterized as support particles with hemispherical BaO phases. The structural and energetic properties of BaO units dissolved inside the MgO host and adsorbed on MgO(100) were investigated by density functional theory (DFT) calculations. Moreover, ab initio thermodynamics was used to explore the shape of BaO and MgO particles in a water environment as a function of temperature. The calculations suggest that the spherical shapes of the segregates result from the growth process and become thermodynamically stabilized by surface hydroxylation.
|
|
| 5. |
- Suchorski, Y., et al.
(författare)
-
Surface-structure libraries: multifrequential oscillations in catalytic hydrogen oxidation on rhodium
- 2019
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:7, s. 4217-4227
-
Tidskriftsartikel (refereegranskat)abstract
- Multifrequential oscillating spatiotemporal patterns in the catalytic hydrogen oxidation on rhodium have been observed in situ in the 10 -6 mbar pressure range using photoemission electron microscopy. The effect is manifested by periodic chemical waves, which travel over the polycrystalline Rh surface and change their oscillation frequency while crossing boundaries between different Rh(hkl) domains. Each crystallographically specific μm-sized Rh(hkl) domain exhibits an individual wave pattern and oscillation frequency, despite the global diffusional coupling of the surface reaction, altogether creating a structure library. This unique reaction behavior is attributed to the ability of stepped surfaces of high-Miller-index domains to facilitate the formation of subsurface oxygen, serving as a feedback mechanism of kinetic oscillations. Formation of a network of subsurface oxygen as a result of colliding reaction fronts was observed in situ. Microkinetic model analysis was used to rationalize the observed effects and to reveal the relation between the barriers for surface oxidation and oscillation frequency. Structural limits of the oscillations, the existence range of oscillations, as well as the effect of varying hydrogen pressure are demonstrated.
|
|
