| 1. |
- Abbondanza, Giuseppe, 1991, et al.
(author)
-
Au-Pd Barcode Nanowires with Tailored Lattice Parameters and Segment Lengths for Catalytic Applications
- 2024
-
In: ACS Applied Nano Materials. - 2574-0970. ; 7:4, s. 3861-3874
-
Journal article (peer-reviewed)abstract
- In this study, we present a systematic investigation of the controlled fabrication of Au-Pd barcode nanowires within nanoporous anodic aluminum oxide (NP-AAO) templates. By using a combination of in situ X-ray diffraction (XRD), focused ion beam scanning electron microscopy (FIB-SEM), and transmission electron microscopy (TEM), we elucidate the influence of template preparation methods on the resulting nanowire properties. The template treatment, involving either pore widening or barrier layer thinning, significantly impacts nanowire growth. Through the analysis of the XRD data, we observe sequential deposition of Au and Pd segments with lattice parameter variations and strain effects. Particularly, the lattice parameters of Au and Pd segments display intricate temporal dependencies, influenced by interfacial effects and strain caused by growth under confinement. FIB-SEM imaging reveals uniform and reproducible nanowire lengths in the template treated with pore widening. Furthermore, TEM analysis confirms the presence of distinct Au and Pd segments, while scanning TEM-energy-dispersive X-ray spectroscopy revealed minor evidence of interdiffusion between the first and the second electrodeposited segments. Our findings emphasize the potential of the electrodeposition process within nanoporous templates for producing barcode nanowires with precise segmental properties. The combination of in situ XRD and electron microscopy offers valuable insights into the growth dynamics and structural characteristics of the fabricated Au-Pd barcode nanowires. This controlled fabrication strategy opens doors to tailoring nanowire properties for diverse applications, particularly in catalysis.
|
|
| 2. |
- Abbondanza, Giuseppe, 1991, et al.
(author)
-
Hydride formation and dynamic phase changes during template-assisted Pd electrodeposition
- 2023
-
In: Nanotechnology. - 1361-6528 .- 0957-4484. ; 34:50
-
Journal article (peer-reviewed)abstract
- We investigated the structural evolution of electrochemically fabricated Pd nanowires in situ by means of grazing-incidence transmission small- and wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF) and two-dimensional surface optical reflectance (2D-SOR). This shows how electrodeposition and the hydrogen evolution reaction (HER) compete and interact during Pd electrodepositon. During the bottom-up growth of the nanowires, we show that beta-phase Pd hydride is formed. Suspending the electrodeposition then leads to a phase transition from beta-phase Pd hydride to alpha-phase Pd. Additionally, we find that grain coalescence later hinders the incorporation of hydrogen in the Pd unit cell. GTSAXS and 2D-SOR provide complementary information on the volume fraction of the pores occupied by Pd, while XRF was used to monitor the amount of Pd electrodeposited.
|
|
| 3. |
- Blomberg, Sara, et al.
(author)
-
Combining synchrotron light with laser technology in catalysis research
- 2018
-
In: Journal of Synchrotron Radiation. - 1600-5775 .- 0909-0495. ; 25:5, s. 1389-1394
-
Journal article (peer-reviewed)abstract
- High-energy surface X-ray diffraction (HESXRD) provides surface structural information with high temporal resolution, facilitating the understanding of the surface dynamics and structure of the active phase of catalytic surfaces. The surface structure detected during the reaction is sensitive to the composition of the gas phase close to the catalyst surface, and the catalytic activity of the sample itself may affect the surface structure, which in turn may complicate the assignment of the active phase. For this reason, planar laser-induced fluorescence (PLIF) and HESXRD have been combined during the oxidation of CO over a Pd(100) crystal. PLIF complements the structural studies with an instantaneous two-dimensional image of the CO2 gas phase in the vicinity of the active model catalyst. Here the combined HESXRD and PLIF operandomeasurements of CO oxidation over Pd(100) are presented, allowing for an improved assignment of the correlation between sample structure and the CO2distribution above the sample surface with sub-second time resolution.
|
|
| 4. |
- Blomberg, Sara, et al.
(author)
-
Generation and oxidation of aerosol deposited PdAg nanoparticles
- 2013
-
In: Surface Science. - : Elsevier BV. - 0039-6028. ; 616, s. 186-191
-
Journal article (peer-reviewed)abstract
- PdAg nanoparticles with a diameter of 10 nm have been generated by an aerosol particle method, and supported on a silica substrate. By using a combination of X-ray Energy Dispersive Spectroscopy and X-ray Photoelectron Spectroscopy it is shown that the size distribution of the particles is narrow and that the two metals form an alloy with a mixture of 75% Pd and 25% Ag. Under oxidizing conditions, Pd is found to segregate to the surface and a thin PdO like oxide is formed similar to the surface oxide previously reported on extended PdAg and pure Pd surfaces. (C) 2013 Elsevier B.V. All rights reserved.
|
|
| 5. |
- Blomberg, Sara, et al.
(author)
-
Strain Dependent Light-off Temperature in Catalysis Revealed by Planar Laser-Induced Fluorescence
- 2017
-
In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 7:1, s. 110-114
-
Journal article (peer-reviewed)abstract
- Understanding how specific atom sites on metal surfaces lower the energy barrier for chemical reactions is vital in catalysis. Studies on simplified model systems have shown that atoms arranged as steps on the surface play an important role in catalytic reactions, but a direct comparison of how the light-off temperature is affected by the atom orientation on the step has not yet been possible due to methodological constraints. Here we report in situ spatially resolved measurements of the CO2 production over a cylindrical-shaped Pd catalyst and show that the light-off temperature at different parts of the crystal depends on the step orientation of the two types of steps (named A and B). Our finding is supported by density functional theory calculations, revealing that the steps, in contrast to what has been previously reported in the literature, are not directly involved in the reaction onset but have the role of releasing stress.
|
|
| 6. |
- Busch, Michael, 1983, et al.
(author)
-
Adsorption of NO on Fe3O4(111)
- 2018
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 693, s. 84-87
-
Journal article (peer-reviewed)abstract
- Adsorption of NO on Fe 3 O 4 (111) is studied by density functional theory (DFT) calculations. NO is preferably adsorbed atop the octahedral site which has a clearly higher adsorption energy than the tetrahedral site. The difference in adsorption energy correlates with differences in adsorption geometries and N–O stretch vibrations. The results are in good agreement with temperature programmed desorption (TPD) and reflection-adsorption IR spectroscopy (RAIRS) measurements and provide an explanation of the observation of only one vibrational mode despite two distinct TPD features.
|
|
| 7. |
- Gajdek, Dorotea, et al.
(author)
-
Structural Changes in Monolayer Cobalt Oxides under Ambient Pressure CO and O 2 Studied by In Situ Grazing-Incidence X-ray Absorption Fine Structure Spectroscopy
- 2022
-
In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:7, s. 3411-3418
-
Journal article (peer-reviewed)abstract
- We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge to characterize monolayer CoO films on Pt(111) under ambient pressure exposure to CO and O2, with the aim of identifying the Co phases present and their transformations under oxidizing and reducing conditions. X-ray absorption near edge structure (XANES) spectra show clear changes in the chemical state of Co, with the 2+ state predominant under CO exposure and the 3+ state predominant under O2-rich conditions. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis shows that the CoO bilayer characterized in ultrahigh vacuum is not formed under the conditions used in this study. Instead, the spectra acquired at low temperatures suggest formation of cobalt hydroxide and oxyhydroxide. At higher temperatures, the spectra indicate dewetting of the film and suggest formation of bulklike Co3O4 under oxidizing conditions. The experiments demonstrate the power of hard X-ray spectroscopy to probe the structures of well-defined oxide monolayers on metal single crystals under realistic catalytic conditions.
|
|
| 8. |
- Garcia-Martinez, Fernando, et al.
(author)
-
Reduced Carbon Monoxide Saturation Coverage on Vicinal Palladium Surfaces: The Importance of the Adsorption Site
- 2021
-
In: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:39, s. 9508-9515
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 9. |
- Garcia-Martinez, Fernando, et al.
(author)
-
Structure Matters: Asymmetric CO Oxidation at Rh Steps with Different Atomic Packing
- 2022
-
In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 144:33, s. 15363-15371
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 10. |
- Grönbeck, Henrik, 1966, et al.
(author)
-
Mechanism for reversed photoemission core-level shifts of oxidized Ag
- 2012
-
In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 85:11
-
Journal article (peer-reviewed)abstract
- Density functional theory calculations and high-resolution core-level spectroscopy are used to explore the remarkable observation of decreased Ag 3d binding energy upon silver oxidation. The shift in Ag 3d binding energy is investigated at different degrees of oxidation and compared to results for Pd 3d, which exhibits a normal shift. Analysis of initial-state effects and valence electronic structure shows that the onsite Ag core potential is insensitive to oxidation despite a clear metal-to-oxygen charge transfer. The substantial negative shift for oxidized Ag is instead attributed to final-state effects as screening of the core-hole occurs in metal s states of bonding character.
|
|
