A5035963338- Catalytic Processes in Materials Science
- Advanced Chemical Physics Studies
- Catalysis and Oxidation Reactions
- nanoparticles nucleation surface interactions
- Electronic and Structural Properties of Oxides
- Copper-based nanomaterials and applications
- Magnetic properties of thin films
- Catalysts for Methane Reforming
- Electron and X-Ray Spectroscopy Techniques
- Advanced Materials Characterization Techniques
- Spectroscopy and Laser Applications
- Surface and Thin Film Phenomena
- Iron oxide chemistry and applications
- Electrocatalysts for Energy Conversion
- ZnO doping and properties
- X-ray Spectroscopy and Fluorescence Analysis
- Surface Chemistry and Catalysis
- Nanomaterials for catalytic reactions
- Catalysis and Hydrodesulfurization Studies
- Semiconductor materials and devices
- Atmospheric chemistry and aerosols
- Theoretical and Computational Physics
- Coagulation and Flocculation Studies
- Magnetic Properties and Synthesis of Ferrites
- Semiconductor Quantum Structures and Devices
Lund University
2015-2024
Material Physics Center
2020
Brookhaven National Laboratory
2020
University of the Basque Country
2020
Donostia International Physics Center
2020
National Synchrotron Radiation Research Center
2002-2017
Uppsala University
2017
University of St Andrews
2008-2015
KTH Royal Institute of Technology
2014
Colorado State University
2011
The oxidation of the Pd(100) surface at oxygen pressures in 10(-6) to 10(3) mbar range and temperatures up 1000 K has been studied situ by x-ray diffraction (SXRD). results provide direct structural information on phases present region kinetics oxide formation. Depending (T,p) environmental conditions, we observe either a thin (sqrt[5]xsqrt[5])R27 degrees or growth rough, poorly ordered bulk film PdO predominantly with (001) orientation. By comparison phase diagram from first-principles...
The oxidation of the Rh(111) surface at oxygen pressures from ${10}^{\ensuremath{-}10}\text{ }\mathrm{mbar}$ to 0.5 bar and temperatures between 300 900 K has been studied on atomic scale using a multimethod approach experimental theoretical techniques. Oxidation starts steps, resulting in trilayer O-Rh-O oxide which, although not thermodynamically stable, prevents further intermediate pressures. A thick corundum like ${\mathrm{Rh}}_{2}{\mathrm{O}}_{3}$ bulk is formed only significantly...
The active phase of Pd during methane oxidation is a long-standing puzzle, which, if solved, could provide routes for design improved catalysts. Here, density functional theory and in situ surface X-ray diffraction are used to identify characterize atomic sites yielding high conversion. Calculations performed dissociation over range PdOx surfaces reveal facile on either under-coordinated PdO(101) or metallic surfaces. experiments show unambiguously that conversion requires sufficiently thick...
Understanding the interaction between surfaces and their surroundings is crucial in many materials-science fields, such as catalysis, corrosion, thin-film electronics, but existing characterization methods have not been capable of fully determining structure during dynamic processes, catalytic reactions, a reasonable time frame. We demonstrate an x-ray-diffraction-based method that uses high-energy photons (85 kiloelectron volts) to provide unexpected gains data acquisition speed by several...
We present high-pressure x-ray photoelectron spectroscopy (HP-XPS) and first-principles kinetic Monte Carlo study addressing the nature of active surface in CO oxidation over Pd(100). Simultaneously measuring chemical composition at near-surface gas phase, we reveal both O-covered pristine Pd(100) a oxide as stable, highly phases near-ambient regime accessible to HP-XPS. Surprisingly, no adsorbed can be detected during high ${\mathrm{CO}}_{2}$ production rates, which explained by combination...
Time-resolved in situ, energy-dispersive X-ray absorption spectroscopy and mass spectrometry are used to correlate changes the chemical state of alumina- ceria-supported palladium nanoparticles with activity selectivity for methane oxidation. Specifically, modulation excitation experiments carried out by periodically cycling between net-reducing net-oxidizing reaction conditions. The XANES EXAFS data show that readily bulk-oxidized when exposed oxygen, forming a PdO-like phase, reduced back...
CO2 reduction reactions, which provide one route to limit the emission of this greenhouse gas, are commonly performed over Cu-based catalysts. Here, we use ambient pressure X-ray photoelectron spectroscopy together with density functional theory obtain an atomistic understanding dissociative adsorption on Cu(100). We find that process is dominated by presence steps, promote both a lowering dissociation barrier and efficient separation between adsorbed O CO, reducing probability for...
Catalytic CO oxidation is a seemingly simple reaction between and O2 molecules, one of the reactions in automotive catalytic converters, fruit-fly model catalysis. Surprisingly, phase responsible for activity still under debate, despite decades investigations. We have performed but yet conclusive study single crystal Rh Pd catalysts, resolving this controversy. For Rh, oxygen-covered metallic surface more active than oxide, while Pd, thin oxide films are at least as surface, thicker less...
HIPPIE is a soft X-ray beamline on the 3 GeV electron storage ring of MAX IV Laboratory, equipped with novel ambient-pressure photoelectron spectroscopy (APXPS) instrument. The endstation dedicated to performing in situ and operando experiments presence controlled gaseous atmosphere at pressures up 30 mbar [1 = 100 Pa] as well under ultra-high-vacuum conditions. photon energy range 250 2200 eV planar polarization fluxes >10 12 photons s −1 (500 mA current) resolving power greater than...
The structure of the oxygen-induced p(4 x 4) reconstruction Ag(111) is determined by a combination scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models this are incorrect propose new model which able to explain our experimental findings but has no resemblance bulk silver oxide. also shed some light on limitations current theories potential role van der Waals interactions in stabilization...
Using core-level spectroscopy and density functional theory we show that a one-dimensional (1D) oxide structure forms at the steps of Pt(332) surface after exposure. The 1D is found to be stable in an oxygen pressure range, where bulk oxides are only metastable, therefore argued precursor Pt oxidation. As example consequences such exclusively present steps, investigate reaction CO with covered Pt(332). Albeit more strongly bound, oxidic react easily than chemisorbed on terraces.
The surface structure of Pd(100) during CO oxidation was measured using a combination flow reactor and in situ X-ray diffraction coupled to large-area 2-dimensional detector. for P(O(2))/P(CO) ratios between 0.6 10 at fixed total gas pressure 200 mbar ± 1 mbar. In conjunction with the reactivity also determined. For all found oxidize above certain temperature. Three different types oxides were observed: oxide, an epitaxial layer bulk-like PdO, non-epitaxial PdO. As soon as oxide present be...
High-pressure X-ray photoelectron spectroscopy, mass spectrometry, and density functional theory calculations have been combined to study methane oxidation over Pd(100). The measurements reveal a high activity when two-layer PdO(101) oriented film is formed. Although one-layer exhibits similar surface structure, no or very little observed. show that the presence of an oxygen atom directly below coordinatively unsaturated Pd in crucial for efficient dissociation, demonstrating ligand effect...
Using a combination of surface X-ray diffraction and mass spectrometry at realistic pressures, the CO oxidation reactivity Rh(111) model catalyst has been studied in conjunction with structure. The measurements show that specific thin oxide is always present high activity regime Rh-based oxidation.
Using in situ high-pressure x-ray photoelectron spectroscopy, we have followed the oxidation and reduction of Pd model catalysts oxygen CO pressures millibar range. The study includes a Pd(100) single crystal as well SiO${}_{x}$-supported nanoparticles 15 or 35 nm diameter, respectively. We demonstrate that also form ultrathin surface oxides prior to onset bulk PdO. are observed oxidize at sample temperatures 40 degrees lower than single-crystal surface. In $3{d}_{5/2}$ O $1s$ spectrum,...
The adsorption of CO on clean and oxidized Pd(111) surfaces has been investigated using a combination high-resolution core level spectroscopy (HRCLS), reflection absorption infrared (RAIRS), density functional theory (DFT) calculations. HRCLS RAIRS measurements reveal that adsorbs Pd(111), Pd5O4 PdO(101) at 100 ± 10 K the coverage decreases with increasing oxidation state Pd for same exposures Langmuirs. Based DFT calculations, layer was found to include molecular in both hollow bridge...
CO<sub>2</sub> methanation over Rh/CeO<sub>2</sub> and Ni/CeO<sub>2</sub> highlighting the different surface speciation during reaction as deduced from our study.
The initial oxidation of Rh(100) has been studied using high resolution core level spectroscopy, low energy electron diffraction, surface x-ray scanning tunneling microscopy, and density functional theory. We report a structural study an oxygen induced structure displaying $c(8\ifmmode\times\else\texttimes\fi{}2)$ periodicity at pressure above ${10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}\mathrm{mbar}$ sample temperature $700\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Our experimental...
Using a combination of surface x-ray diffraction and mass spectrometry at realistic pressures, the CO oxidation reactivity Rh(111) Rh(100) model catalysts has been studied in conjunction with structure. The measurements show that presence specific thin oxide is crucial for high activity Rh based oxidation. As this readily formed on all facets, we conclude crystal planes exposed during catalysis will not directly influence reactivity. This fortified by very close similarity between results.
Surface chemistry and catalysis studies could significantly gain from the systematic variation of surface active sites, tested under very same conditions. Curved crystals are excellent platforms to perform such systematics, which may in turn allow better resolve fundamental properties reveal new phenomena. This is demonstrated here for carbon monoxide/platinum system. We curve a platinum crystal around high-symmetry (111) direction carry out photoemission scans on top. renders spatial...
We investigated the intrinsic reactivity of CO on single-layer and multilayer PdO(101) grown Pd(100) using temperature-programmed reaction spectroscopy (TPRS) reflection absorption infrared (RAIRS) experiments, as well density functional theory (DFT) calculations. find that binds more strongly than (∼119 kJ/mol vs 43 kJ/mol), oxidizes negligibly PdO(101), whereas nearly 90% a saturated layer during TPRS experiments. RAIRS further shows molecules adsorb both bridge-Pdcus atop-Pdcus sites...
The oxidation of a vicinal Pd(553) surface has been studied from ultrahigh vacuum (UHV) to atmospheric oxygen pressures at elevated sample temperatures. investigation combines traditional electron based UHV techniques such as high resolution core level spectroscopy, low-energy diffraction, scanning tunneling microscopy with in situ x-ray and ab initio simulations. In this way, we show that the O atoms preferentially adsorb step edges below...