Publications by authors named "Zdenek Jakub"
In polarizable materials, electronic charge carriers interact with the surrounding ions, leading to quasiparticle behavior. The resulting polarons play a central role in many materials properties including electrical transport, interaction with light, surface reactivity, and magnetoresistance, and polarons are typically investigated indirectly through these macroscopic characteristics. Here, noncontact atomic force microscopy (nc-AFM) is used to directly image polarons in FeO at the single quasiparticle limit.
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- The study focuses on how single-atom catalysts coordinate reactants at their active sites, specifically using Rh adatoms and Rh dimers on FeO(001) when exposed to CO.
- Time-lapse scanning tunneling microscopy (STM) reveals that Rh atoms adapt their structure to form stable RhCO monocarbonyls and occasionally Rh(CO) gem-dicarbonyls, which require breaking down Rh dimers.
- The findings highlight the importance of minority species, often overlooked, in catalytic processes and demonstrate that the breakdown of dimers can lead to the formation of reactive configurations in single-atom catalysis.
The functionality of 2D metal-organic frameworks (MOFs) is crucially dependent on the local environment of the embedded metal atoms. These atomic-scale details are best ascertained on MOFs supported on well-defined surfaces, but the interaction with the support often changes the MOF properties. We elucidate the extent of this effect by comparing the Fe-TCNQ 2D MOF on two weakly interacting supports: graphene and Au(111).
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- The (111) facet of magnetite (FeO) has been widely researched, with ongoing debates about the true low-energy surface structures.
- Using density functional theory (DFT), three new surface reconstructions have been identified as more stable than the previously accepted structure, particularly in reducing environments.
- Microscopy techniques reveal a specific structure consisting of tetrahedral iron and 3-fold coordinated oxygen, which clarifies why certain areas are chemically inactive.
Article Synopsis
- * This study uses density functional theory and surface experiments to investigate how Rh, Pt, and Au metals interact with reduced TiO(110) surfaces, identifying different coupling behaviors influenced by polarons.
- * It finds that Pt and Au strongly interact with oxygen vacancy sites, resulting in charge transfer and metal reduction, while Rh has weaker interactions, indicating a complex relationship between adatoms, vacancies, and polarons essential for understanding single-atom catalysts.
Article Synopsis
- Polarizable materials, like KTaO, are important in catalysis due to their ability to modify chemical reactivity through surface properties.
- The study highlights how KTaO's surfaces, which have different terminations, create unique environments for carbon monoxide (CO) molecules, affecting their charge and binding strength.
- Results indicate that the presence of excess charge on TaO terraces leads to stronger interactions with CO, demonstrating a link between adsorption states and ferroelectric polarization.
Potential applications of 2D metal-organic frameworks (MOF) require the frameworks to be monophase and well-defined at the atomic scale, to be decoupled from the supporting substrate, and to remain stable at the application conditions. Here, we present three systems meeting this elusive set of requirements: M-TCNQ (M = Ni, Fe, Mn) on epitaxial graphene/Ir(111). We study the systems experimentally by scanning tunneling microscopy, low energy electron microscopy and X-ray photoelectron spectroscopy.
View Article and Find Full Text PDFHeterogeneous catalysts based on subnanometer metal clusters often exhibit strongly size-dependent properties, and the addition or removal of a single atom can make all the difference. Identifying the most active species and deciphering the reaction mechanism is extremely difficult, however, because it is often not clear how the catalyst evolves in operando. Here, we use a combination of atomically resolved scanning probe microscopies, spectroscopic techniques, and density functional theory (DFT)-based calculations to study CO oxidation by a model Pt/FeO(001) "single-atom" catalyst.
View Article and Find Full Text PDFOxide-supported single-atom catalysts are commonly modeled as a metal atom substituting surface cation sites in a low-index surface. Adatoms with dangling bonds will inevitably coordinate molecules from the gas phase, and adsorbates such as water can affect both stability and catalytic activity. Herein, we use scanning tunneling microscopy (STM), noncontact atomic force microscopy (ncAFM), and X-ray photoelectron spectroscopy (XPS) to show that high densities of single Rh adatoms are stabilized on α-FeO(11̅02) in the presence of 2 × 10 mbar of water at room temperature, in marked contrast to the rapid sintering observed under UHV conditions.
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- Oxygen exchange at interfaces of oxides is crucial for understanding catalytic activity and material degradation, but the atomic details are often unclear.
- New findings reveal that stable, defect-free surfaces can reactively exchange oxygen with water vapor quickly at temperatures below 70°C without altering their atomic structure.
- This exchange occurs mainly during the final stages of water desorption and involves a process where the stability of a specific hydrogen-oxygen complex offsets the energy costs of extracting lattice oxygen, offering insights valuable for various scientific fields.
Article Synopsis
- The stability and reactivity of single-atom catalysts are influenced by their local environment, which is still not fully understood.
- An in-depth study of various metal atoms (like gold and platinum) on a model support (FeO(001)) revealed that their ability to adsorb carbon monoxide (CO) varies significantly from bulk metal surfaces.
- The interaction between the metal and the support alters electronic properties, affecting bond strength, while structural distortions also play a key role in determining CO adsorption energies.
Article Synopsis
- The study investigates how the structure of a Rh/FeO(001) catalyst changes during CO oxidation, focusing on the different outcomes based on whether O or CO is adsorbed first.
- When oxygen is added first, it destabilizes Rh atoms, causing them to form RhO clusters that effectively catalyze oxidation at relatively low temperatures (around 200 K).
- In contrast, if carbon monoxide is introduced first, it prevents effective interaction with oxygen, resulting in a less efficient oxidation process that relies on a different mechanism at higher temperatures (480 K).
Atomic-scale investigations of metal oxide surfaces exposed to aqueous environments are vital to understand degradation phenomena (e.g., dissolution and corrosion) as well as the performance of these materials in applications.
View Article and Find Full Text PDFLocal Structure and Coordination Define Adsorption in a Model Ir /Fe O Single-Atom Catalyst.
Angew Chem Int Ed Engl
September 2019
Article Synopsis
- Single-atom catalysts (SACs) combine features of both homo- and heterogeneous catalysis, with metal atoms influenced by their surrounding ligands impacting reactant adsorption.
- A range of advanced techniques, including microscopy and spectroscopy, were used to analyze CO binding on different iridium (Ir) sites supported by iron oxide (Fe O) at various temperatures.
- Findings revealed that Ir adatoms bind CO more effectively in specific coordinated states and suggested that higher temperatures lead to Ir incorporation into the support and eventual agglomeration into inactive nanoparticles, highlighting an important deactivation mechanism.
The interaction of water with the most prominent surfaces of FeO, (001) and (111), is directly compared using a combination of temperature-programmed desorption, temperature-programmed low energy electron diffraction (TP LEED), and scanning probe microscopies. Adsorption on the (√2 × √2)R45°-reconstructed surface of FeO(001) is strongly influenced by the surface reconstruction, which remains intact at all coverages. Close to the completion of the first monolayer, however, the ad-layer adopts a longer-range (2 × 2) superstructure.
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- - Determining how water interacts with solid surfaces, specifically on FeO(001), is challenging due to the complexity of the water structures formed.
- - Water forms partially dissociated dimers at low coverage, which then facilitate the growth of trimers and eventually a hydrogen-bonded network as more water molecules are added.
- - Advanced techniques like temperature-programmed desorption, X-ray photoelectron spectroscopy, and atomic force microscopy are crucial for analyzing these structures and validating theoretical models of their lowest energy configurations.
Atomic-Scale Structure of the Hematite α-FeO(11̅02) "R-Cut" Surface.
J Phys Chem C Nanomater Interfaces
January 2018
The α-FeO(11̅02) surface (also known as the hematite r-cut or (012) surface) was studied using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STM), noncontact atomic force microscopy (nc-AFM), and density functional theory (DFT)+ calculations. Two surface structures are stable under ultrahigh vacuum (UHV) conditions; a stoichiometric (1 × 1) surface can be prepared by annealing at 450 °C in ≈10 mbar O, and a reduced (2 × 1) reconstruction is formed by UHV annealing at 540 °C. The (1 × 1) surface is close to an ideal bulk termination, and the undercoordinated surface Fe atoms reduce the surface bandgap by ≈0.
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- Scientists need to understand how catalysts are shaped to know how they work in reactions, but it's hard to figure out the best methods to study them.
- Researchers used a special technique called NIXSW to find out the exact positions of silver (Ag) and copper (Cu) atoms on a surface called FeO(001).
- They discovered that while both types of atoms are in similar places, silver is higher up than copper, and some calculations were better at predicting this than others.
The interaction of CO with the FeO(001)-(√2 × √2)R45° surface was studied using temperature-programmed desorption (TPD), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS), the latter both under ultrahigh vacuum (UHV) conditions and in CO pressures up to 1 mbar. In general, the CO-FeO interaction is found to be weak. The strongest adsorption occurs at surface defects, leading to small TPD peaks at 115, 130, and 190 K.
View Article and Find Full Text PDFThe adsorption of CO on the FeO(001)-(2 × 2)R45° surface was studied experimentally using temperature programmed desorption (TPD), photoelectron spectroscopies (UPS and XPS), and scanning tunneling microscopy. CO binds most strongly at defects related to Fe, including antiphase domain boundaries in the surface reconstruction and above incorporated Fe interstitials. At higher coverages,CO adsorbs at fivefold-coordinated Fe sites with a binding energy of 0.
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