Prof. Dr. Barbara Lechner
Academic Research Focus
- Operando microscopy (NAP-STM) and spectroscopy (NAP-XPS) methods for catalytic systems
- Reactions on oxide-supported size-selected clusters as model systems
- Video-rate scanning tunneling microscopy (FastSTM) under near ambient pressure (NAP)
- Reactions on oxide-supported size-selected clusters as model systems
- Video-rate scanning tunneling microscopy (FastSTM) under near ambient pressure (NAP)
Fields of Application
Nanomaterials, Photo-(electro)catalysis
Publications
14.
J Reich, S Kaiser, A Bourgund, M Krinninger, U Heiz, F Esch, B A J Lechner
Exploring the atomic-scale dynamics of Fe3O4(001) at catalytically relevant temperatures using FastSTM Journal Article
In: Surface Science, vol. 752, pp. 122634, 2025, ISSN: 0039-6028.
@article{nokey,
title = {Exploring the atomic-scale dynamics of Fe3O4(001) at catalytically relevant temperatures using FastSTM},
author = {J Reich and S Kaiser and A Bourgund and M Krinninger and U Heiz and F Esch and B A J Lechner},
url = {https://www.sciencedirect.com/science/article/pii/S0039602824001857},
doi = {https://doi.org/10.1016/j.susc.2024.122634},
issn = {0039-6028},
year = {2025},
date = {2025-02-01},
urldate = {2025-02-01},
journal = {Surface Science},
volume = {752},
pages = {122634},
abstract = {Surfaces and interfaces of functional nanoscale materials are typically highly dynamic when employed at elevated temperatures. Both, lateral surface and vertical bulk exchange diffusion processes set in, which can be relevant for applications such as heterogeneous catalysis. Time-resolved scanning tunneling microscopy (STM) is being pushed to ever faster measurement modes to follow such dynamic phenomena in situ. Here, we present FastSTM movies monitoring a range of atomic-scale dynamics of a prototypical reducible oxide catalyst support, Fe3O4(001), at elevated temperatures. Antiphase domain boundaries between two domains of the reconstructed surface exhibit local mobility from around 350 K, while Fe-rich point defects, in a stable equilibrium with the bulk, appear to diffuse in a peculiar zigzag pattern above 500 K. Finally, exploiting the diffusivity of Fe interstitials, we follow the propagation of step edges in the topmost atomic layer of the Fe3O4(001) surface in an oxygen atmosphere.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Surfaces and interfaces of functional nanoscale materials are typically highly dynamic when employed at elevated temperatures. Both, lateral surface and vertical bulk exchange diffusion processes set in, which can be relevant for applications such as heterogeneous catalysis. Time-resolved scanning tunneling microscopy (STM) is being pushed to ever faster measurement modes to follow such dynamic phenomena in situ. Here, we present FastSTM movies monitoring a range of atomic-scale dynamics of a prototypical reducible oxide catalyst support, Fe3O4(001), at elevated temperatures. Antiphase domain boundaries between two domains of the reconstructed surface exhibit local mobility from around 350 K, while Fe-rich point defects, in a stable equilibrium with the bulk, appear to diffuse in a peculiar zigzag pattern above 500 K. Finally, exploiting the diffusivity of Fe interstitials, we follow the propagation of step edges in the topmost atomic layer of the Fe3O4(001) surface in an oxygen atmosphere.
13.
F Kraushofer, M Krinninger, S Kaiser, J Reich, A Jarosz, M Füchsl, G Anand, F Esch, B A J Lechner
The influence of bulk stoichiometry on near-ambient pressure reactivity of bare and Pt-loaded rutile TiO2(110) Journal Article
In: Nanoscale, vol. 16, no. 38, pp. 17825-17837, 2024, ISSN: 2040-3364.
@article{nokey,
title = {The influence of bulk stoichiometry on near-ambient pressure reactivity of bare and Pt-loaded rutile TiO2(110)},
author = {F Kraushofer and M Krinninger and S Kaiser and J Reich and A Jarosz and M F\"{u}chsl and G Anand and F Esch and B A J Lechner},
url = {http://dx.doi.org/10.1039/D4NR01702A},
doi = {10.1039/D4NR01702A},
issn = {2040-3364},
year = {2024},
date = {2024-08-29},
urldate = {2024-08-29},
journal = {Nanoscale},
volume = {16},
number = {38},
pages = {17825-17837},
abstract = {The interaction of catalyst particles with reducible support materials can drastically change their reactivity. On rutile TiO2, processes like particle encapsulation (caused by the “strong metal\textendashsupport interaction”, SMSI) have long been known to depend on the initial reduction state of the oxide. Despite this knowledge, sample stoichiometry has rarely been controlled in a reproducible manner in the surface science literature. Here, we use scanning tunnelling microscopy (STM) to explore systematically how near-ambient pressures (0.1\textendash1.0 mbar) of O2, H2, CO and CO2 affect blank and Pt-loaded rutile TiO2(110) surfaces of different bulk stoichiometry at 600 K. To this end, we present preparation recipes that result in a sample stoichiometry always converging back to the same value, which allows us to use the same samples with constant reduction state over hundreds of preparation cycles. Comparing a highly reduced and a near-stoichiometric TiO2 sample, we find that surface reactivity to all four gasses differs even without Pt loading. Most surprisingly, we find that the highly reduced TiO2(110) is oxidized by CO2, but this reaction is completely inhibited on the near-stoichiometric sample. Pt nanoparticles, in turn, become encapsulated after vacuum annealing on the reduced, but not on the near-stoichiometric sample. Encapsulation on the near-stoichiometric sample is achieved only after exposing it to 0.1 mbar H2 at 600 K. Interestingly, we also see a further modification of the already encapsulated particles on the reduced sample under the same conditions, such that they become embedded deeper in the TiO2(110) surface.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The interaction of catalyst particles with reducible support materials can drastically change their reactivity. On rutile TiO2, processes like particle encapsulation (caused by the “strong metal–support interaction”, SMSI) have long been known to depend on the initial reduction state of the oxide. Despite this knowledge, sample stoichiometry has rarely been controlled in a reproducible manner in the surface science literature. Here, we use scanning tunnelling microscopy (STM) to explore systematically how near-ambient pressures (0.1–1.0 mbar) of O2, H2, CO and CO2 affect blank and Pt-loaded rutile TiO2(110) surfaces of different bulk stoichiometry at 600 K. To this end, we present preparation recipes that result in a sample stoichiometry always converging back to the same value, which allows us to use the same samples with constant reduction state over hundreds of preparation cycles. Comparing a highly reduced and a near-stoichiometric TiO2 sample, we find that surface reactivity to all four gasses differs even without Pt loading. Most surprisingly, we find that the highly reduced TiO2(110) is oxidized by CO2, but this reaction is completely inhibited on the near-stoichiometric sample. Pt nanoparticles, in turn, become encapsulated after vacuum annealing on the reduced, but not on the near-stoichiometric sample. Encapsulation on the near-stoichiometric sample is achieved only after exposing it to 0.1 mbar H2 at 600 K. Interestingly, we also see a further modification of the already encapsulated particles on the reduced sample under the same conditions, such that they become embedded deeper in the TiO2(110) surface.
12.
M Krinninger, F Kraushofer, N B Refvik, M Blum, B A J Lechner
Interface Effects in the Stability of 2D Silica, Silicide, and Silicene on Pt(111) and Rh(111) Journal Article
In: ACS Applied Materials & Interfaces, vol. 16, no. 21, pp. 27481-27489, 2024, ISSN: 1944-8244.
@article{nokey,
title = {Interface Effects in the Stability of 2D Silica, Silicide, and Silicene on Pt(111) and Rh(111)},
author = {M Krinninger and F Kraushofer and N B Refvik and M Blum and B A J Lechner},
url = {https://doi.org/10.1021/acsami.4c05137},
doi = {10.1021/acsami.4c05137},
issn = {1944-8244},
year = {2024},
date = {2024-05-29},
urldate = {2024-05-29},
journal = {ACS Applied Materials \& Interfaces},
volume = {16},
number = {21},
pages = {27481-27489},
abstract = {Ultrathin two-dimensional silica films have been suggested as highly defined conductive models for fundamental studies on silica-supported catalyst particles. Key requirements in this context are closed silica films that isolate the gas phase from the underlying metal substrate and stability under reaction conditions. Here, we present silica bilayer films grown on Pt(111) and Rh(111) and characterize them by scanning tunneling microscopy and X-ray photoelectron spectroscopy. We provide the first report of silica bilayer films on Rh(111) and have further successfully prepared fully closed films on Pt(111). Interestingly, surface and interface silicide phases play a decisive role in both cases: On platinum, closed films can be stabilized only when silicon is deposited in excess, which results in an interfacial silicide or silicate layer. We show that these silica films can also be grown directly from a surface silicide phase. In the case of rhodium, the silica phase is less stable and can be reduced to a silicide in reductive environments. Though similar in appearance to the “silicene” phases that have been controversially discussed on Ag(111), we conclude that an interpretation of the phase as a surface silicide is more consistent with our data. Finally, we show that the silica film on platinum is stable in 0.8 mbar CO but unstable at elevated temperatures. We thus conclude that these systems are only suitable as model catalyst supports to a limited extent.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ultrathin two-dimensional silica films have been suggested as highly defined conductive models for fundamental studies on silica-supported catalyst particles. Key requirements in this context are closed silica films that isolate the gas phase from the underlying metal substrate and stability under reaction conditions. Here, we present silica bilayer films grown on Pt(111) and Rh(111) and characterize them by scanning tunneling microscopy and X-ray photoelectron spectroscopy. We provide the first report of silica bilayer films on Rh(111) and have further successfully prepared fully closed films on Pt(111). Interestingly, surface and interface silicide phases play a decisive role in both cases: On platinum, closed films can be stabilized only when silicon is deposited in excess, which results in an interfacial silicide or silicate layer. We show that these silica films can also be grown directly from a surface silicide phase. In the case of rhodium, the silica phase is less stable and can be reduced to a silicide in reductive environments. Though similar in appearance to the “silicene” phases that have been controversially discussed on Ag(111), we conclude that an interpretation of the phase as a surface silicide is more consistent with our data. Finally, we show that the silica film on platinum is stable in 0.8 mbar CO but unstable at elevated temperatures. We thus conclude that these systems are only suitable as model catalyst supports to a limited extent.
11.
J Reich, S Kaiser, U Heiz, J-D Grunwaldt, M M Kappes, F Esch, B A J Lechner
A Critical View on the Quantification of Model Catalyst Activity Journal Article
In: Topics in Catalysis, vol. 67, no. 13, pp. 880-891, 2024, ISSN: 1572-9028.
@article{nokey,
title = {A Critical View on the Quantification of Model Catalyst Activity},
author = {J Reich and S Kaiser and U Heiz and J-D Grunwaldt and M M Kappes and F Esch and B A J Lechner},
url = {https://doi.org/10.1007/s11244-024-01920-0},
doi = {10.1007/s11244-024-01920-0},
issn = {1572-9028},
year = {2024},
date = {2024-02-19},
urldate = {2024-02-19},
journal = {Topics in Catalysis},
volume = {67},
number = {13},
pages = {880-891},
abstract = {The conversion of reactants, reaction rate referred to catalyst mass, and turnover frequency (TOF) are values typically employed to compare the activity of different catalysts. However, experimental parameters have to be chosen carefully when systems of different complexity are compared. In order to characterize UHV-based model systems, we use a highly sensitive sniffer setup which allows us to investigate the catalytic activity by combining three different measurement modes: temperature-programmed desorption, continuous flow, and pulsed-reactivity experiments. In this article, we explore the caveats of quantifying catalytic activity in UHV on the well-studied and highly defined reference system of CO oxidation on Pt(111), which we later compare to the same reaction on Pt19 clusters deposited on Fe3O4(001). We demonstrate that we can apply fast heating ramps for TOF quantification, thus inducing as little sintering as possible in the metastable clusters. By changing the reactant ratio, we find transient reactivity effects that influence the TOF, which should be kept in mind when comparing catalysts. In addition, the TOF also depends on the surface coverage that itself is a function of temperature and pressure. At a constant reactant ratio, in the absence of transient effects, however, the TOF scales linearly with total pressure over the entire measured temperature range from 200 to 700 K since the reaction rate is dependent on both reactant partial pressures with temperature-dependent reaction order. When comparing the maximum TOF at this particular reactant ratio, we find a 1.6 times higher maximum TOF for Pt19/Fe3O4(001) than for Pt(111). In addition, pulsed-reactivity measurements help identify purely reaction-limited regimes and allow for a more detailed investigation of limiting reactants over the whole temperature range.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The conversion of reactants, reaction rate referred to catalyst mass, and turnover frequency (TOF) are values typically employed to compare the activity of different catalysts. However, experimental parameters have to be chosen carefully when systems of different complexity are compared. In order to characterize UHV-based model systems, we use a highly sensitive sniffer setup which allows us to investigate the catalytic activity by combining three different measurement modes: temperature-programmed desorption, continuous flow, and pulsed-reactivity experiments. In this article, we explore the caveats of quantifying catalytic activity in UHV on the well-studied and highly defined reference system of CO oxidation on Pt(111), which we later compare to the same reaction on Pt19 clusters deposited on Fe3O4(001). We demonstrate that we can apply fast heating ramps for TOF quantification, thus inducing as little sintering as possible in the metastable clusters. By changing the reactant ratio, we find transient reactivity effects that influence the TOF, which should be kept in mind when comparing catalysts. In addition, the TOF also depends on the surface coverage that itself is a function of temperature and pressure. At a constant reactant ratio, in the absence of transient effects, however, the TOF scales linearly with total pressure over the entire measured temperature range from 200 to 700 K since the reaction rate is dependent on both reactant partial pressures with temperature-dependent reaction order. When comparing the maximum TOF at this particular reactant ratio, we find a 1.6 times higher maximum TOF for Pt19/Fe3O4(001) than for Pt(111). In addition, pulsed-reactivity measurements help identify purely reaction-limited regimes and allow for a more detailed investigation of limiting reactants over the whole temperature range.
10.
M Krinninger, N Bock, S Kaiser, J Reich, T Bruhm, F Haag, F Allegretti, U Heiz, K Köhler, B A J Lechner, F Esch
On-Surface Carbon Nitride Growth from Polymerization of 2,5,8-Triazido-s-heptazine Journal Article
In: Chemistry of Materials, vol. 35, no. 17, pp. 6762-6770, 2023, ISSN: 0897-4756.
@article{nokey,
title = {On-Surface Carbon Nitride Growth from Polymerization of 2,5,8-Triazido-s-heptazine},
author = {M Krinninger and N Bock and S Kaiser and J Reich and T Bruhm and F Haag and F Allegretti and U Heiz and K K\"{o}hler and B A J Lechner and F Esch},
url = {https://doi.org/10.1021/acs.chemmater.3c01030},
doi = {10.1021/acs.chemmater.3c01030},
issn = {0897-4756},
year = {2023},
date = {2023-08-23},
urldate = {2023-08-23},
journal = {Chemistry of Materials},
volume = {35},
number = {17},
pages = {6762-6770},
abstract = {Carbon nitrides have recently come into focus for photo- and thermal catalysis, both as support materials for metal nanoparticles as well as photocatalysts themselves. While many approaches for the synthesis of three-dimensional carbon nitride materials are available, only top-down approaches by exfoliation of powders lead to thin-film flakes of this inherently two-dimensional material. Here, we describe an in situ on-surface synthesis of monolayer 2D carbon nitride films as a first step toward precise combination with other 2D materials. Starting with a single monomer precursor, we show that 2,5,8-triazido-s-heptazine can be evaporated intact, deposited on a single crystalline Au(111) or graphite support, and activated via azide decomposition and subsequent coupling to form a covalent polyheptazine network. We demonstrate that the activation can occur in three pathways, via electrons (X-ray illumination), via photons (UV illumination), and thermally. Our work paves the way to coat materials with extended carbon nitride networks that are, as we show, stable under ambient conditions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Carbon nitrides have recently come into focus for photo- and thermal catalysis, both as support materials for metal nanoparticles as well as photocatalysts themselves. While many approaches for the synthesis of three-dimensional carbon nitride materials are available, only top-down approaches by exfoliation of powders lead to thin-film flakes of this inherently two-dimensional material. Here, we describe an in situ on-surface synthesis of monolayer 2D carbon nitride films as a first step toward precise combination with other 2D materials. Starting with a single monomer precursor, we show that 2,5,8-triazido-s-heptazine can be evaporated intact, deposited on a single crystalline Au(111) or graphite support, and activated via azide decomposition and subsequent coupling to form a covalent polyheptazine network. We demonstrate that the activation can occur in three pathways, via electrons (X-ray illumination), via photons (UV illumination), and thermally. Our work paves the way to coat materials with extended carbon nitride networks that are, as we show, stable under ambient conditions.
9.
S Kaiser, J Plansky, M Krinninger, A Shavorskiy, S Zhu, U Heiz, F Esch, B A J Lechner
Does Cluster Encapsulation Inhibit Sintering? Stabilization of Size-Selected Pt Clusters on Fe3O4(001) by SMSI Journal Article
In: ACS Catalysis, vol. 13, no. 9, pp. 6203-6213, 2023.
@article{nokey,
title = {Does Cluster Encapsulation Inhibit Sintering? Stabilization of Size-Selected Pt Clusters on Fe3O4(001) by SMSI},
author = {S Kaiser and J Plansky and M Krinninger and A Shavorskiy and S Zhu and U Heiz and F Esch and B A J Lechner},
url = {https://doi.org/10.1021/acscatal.3c00448},
doi = {10.1021/acscatal.3c00448},
year = {2023},
date = {2023-04-21},
urldate = {2023-04-21},
journal = {ACS Catalysis},
volume = {13},
number = {9},
pages = {6203-6213},
abstract = {The metastability of supported metal nanoparticles limits their application in heterogeneous catalysis at elevated temperatures due to their tendency to sinter. One strategy to overcome these thermodynamic limits on reducible oxide supports is encapsulation via strong metal\textendashsupport interaction (SMSI). While annealing-induced encapsulation is a well-explored phenomenon for extended nanoparticles, it is as yet unknown whether the same mechanisms hold for subnanometer clusters, where concomitant sintering and alloying might play a significant role. In this article, we explore the encapsulation and stability of size-selected Pt5, Pt10, and Pt19 clusters deposited on Fe3O4(001). In a multimodal approach using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM), we demonstrate that SMSI indeed leads to the formation of a defective, FeO-like conglomerate encapsulating the clusters. By stepwise annealing up to 1023 K, we observe the succession of encapsulation, cluster coalescence, and Ostwald ripening, resulting in square-shaped crystalline Pt particles, independent of the initial cluster size. The respective sintering onset temperatures scale with the cluster footprint and thus size. Remarkably, while small encapsulated clusters can still diffuse as a whole, atom detachment and thus Ostwald ripening are successfully suppressed up to 823 K, i.e., 200 K above the H\"{u}ttig temperature that indicates the thermodynamic stability limit.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The metastability of supported metal nanoparticles limits their application in heterogeneous catalysis at elevated temperatures due to their tendency to sinter. One strategy to overcome these thermodynamic limits on reducible oxide supports is encapsulation via strong metal–support interaction (SMSI). While annealing-induced encapsulation is a well-explored phenomenon for extended nanoparticles, it is as yet unknown whether the same mechanisms hold for subnanometer clusters, where concomitant sintering and alloying might play a significant role. In this article, we explore the encapsulation and stability of size-selected Pt5, Pt10, and Pt19 clusters deposited on Fe3O4(001). In a multimodal approach using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM), we demonstrate that SMSI indeed leads to the formation of a defective, FeO-like conglomerate encapsulating the clusters. By stepwise annealing up to 1023 K, we observe the succession of encapsulation, cluster coalescence, and Ostwald ripening, resulting in square-shaped crystalline Pt particles, independent of the initial cluster size. The respective sintering onset temperatures scale with the cluster footprint and thus size. Remarkably, while small encapsulated clusters can still diffuse as a whole, atom detachment and thus Ostwald ripening are successfully suppressed up to 823 K, i.e., 200 K above the Hüttig temperature that indicates the thermodynamic stability limit.
8.
L Xu, K G Papanikolaou, B A J Lechner, L Je, G A Somorjai, M Salmeron, M Mavrikakis
Formation of active sites on transition metals through reaction-driven migration of surface atoms Journal Article
In: Science, vol. 380, no. 6640, pp. 70-76, 2023.
@article{nokey,
title = {Formation of active sites on transition metals through reaction-driven migration of surface atoms},
author = {L Xu and K G Papanikolaou and B A J Lechner and L Je and G A Somorjai and M Salmeron and M Mavrikakis},
url = {https://www.science.org/doi/abs/10.1126/science.add0089},
doi = {doi:10.1126/science.add0089},
year = {2023},
date = {2023-04-06},
urldate = {2023-04-06},
journal = {Science},
volume = {380},
number = {6640},
pages = {70-76},
abstract = {Adopting low-index single-crystal surfaces as models for metal nanoparticle catalysts has been questioned by the experimental findings of adsorbate-induced formation of subnanometer clusters on several single-crystal surfaces. We used density functional theory calculations to elucidate the conditions that lead to cluster formation and show how adatom formation energies enable efficient screening of the conditions required for adsorbate-induced cluster formation. We studied a combination of eight face-centered cubic transition metals and 18 common surface intermediates and identified systems relevant to catalytic reactions, such as carbon monoxide (CO) oxidation and ammonia (NH3) oxidation. We used kinetic Monte Carlo simulations to elucidate the CO-induced cluster formation process on a copper surface. Scanning tunneling microscopy of CO on a nickel (111) surface that contains steps and dislocations points to the structure sensitivity of this phenomenon. Metal-metal bond breaking that leads to the evolution of catalyst structures under realistic reaction conditions occurs much more broadly than previously thought. In heterogeneous catalysis, it is often assumed that adsorbates have minimal effects on the bonding between surface metal atoms at low temperatures and pressures. Xu et al. used density functional theory to find conditions in which adsorbed molecules can scavenge transition metal atoms by breaking bonds at the surface. These atoms can then form clusters, as observed in kinetic Monte Carlo simulations of carbon monoxide on copper and in scanning tunneling microscopy studies of carbon monoxide on a Ni(111) surface containing steps and dislocations. The reaction mechanisms of several catalytic systems may be dominated by in situ adsorbate-induced active site formation. \textemdashPDS Metal atoms freed from transition metal surfaces during reaction can then form clusters that are catalytically active.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Adopting low-index single-crystal surfaces as models for metal nanoparticle catalysts has been questioned by the experimental findings of adsorbate-induced formation of subnanometer clusters on several single-crystal surfaces. We used density functional theory calculations to elucidate the conditions that lead to cluster formation and show how adatom formation energies enable efficient screening of the conditions required for adsorbate-induced cluster formation. We studied a combination of eight face-centered cubic transition metals and 18 common surface intermediates and identified systems relevant to catalytic reactions, such as carbon monoxide (CO) oxidation and ammonia (NH3) oxidation. We used kinetic Monte Carlo simulations to elucidate the CO-induced cluster formation process on a copper surface. Scanning tunneling microscopy of CO on a nickel (111) surface that contains steps and dislocations points to the structure sensitivity of this phenomenon. Metal-metal bond breaking that leads to the evolution of catalyst structures under realistic reaction conditions occurs much more broadly than previously thought. In heterogeneous catalysis, it is often assumed that adsorbates have minimal effects on the bonding between surface metal atoms at low temperatures and pressures. Xu et al. used density functional theory to find conditions in which adsorbed molecules can scavenge transition metal atoms by breaking bonds at the surface. These atoms can then form clusters, as observed in kinetic Monte Carlo simulations of carbon monoxide on copper and in scanning tunneling microscopy studies of carbon monoxide on a Ni(111) surface containing steps and dislocations. The reaction mechanisms of several catalytic systems may be dominated by in situ adsorbate-induced active site formation. —PDS Metal atoms freed from transition metal surfaces during reaction can then form clusters that are catalytically active.
7.
S Kaiser, J Plansky, M Krinninger, A Shavorskiy, S Zhu, U Heiz, F Esch, B A J Lechner
Does cluster encapsulation inhibit sintering? Stabilization of size-selected Pt clusters on Fe $ _3 $ O $ _4 $(001) by SMSI Journal Article
In: arXiv preprint arXiv:2301.10845, 2023.
@article{nokey,
title = {Does cluster encapsulation inhibit sintering? Stabilization of size-selected Pt clusters on Fe $ _3 $ O $ _4 $(001) by SMSI},
author = {S Kaiser and J Plansky and M Krinninger and A Shavorskiy and S Zhu and U Heiz and F Esch and B A J Lechner},
url = {https://arxiv.org/abs/2301.10845},
doi = {https://doi.org/10.48550/arXiv.2301.10845},
year = {2023},
date = {2023-01-25},
urldate = {2023-01-25},
journal = {arXiv preprint arXiv:2301.10845},
abstract = {The metastability of supported metal nanoparticles limits their application in heterogeneous catalysis at elevated temperatures due to their tendency to sinter. One strategy to overcome these thermodynamic limits on reducible oxide supports is encapsulation via strong metal-support interaction (SMSI). While annealing-induced encapsulation is a well-explored phenomenon for extended nanoparticles, it is as yet unknown whether the same mechanisms hold for sub-nanometer clusters, where concomitant sintering and alloying might play a significant role. In this article, we explore the encapsulation and stability of size-selected Pt5, Pt10 and Pt19 clusters deposited on Fe3O4(001). In a multimodal approach using temperature-programmed desorption (TPD), x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), we demonstrate that SMSI indeed leads to the formation of a defective, FeO-like conglomerate encapsulating the clusters. By stepwise annealing up to 1023 K, we observe the succession of encapsulation, cluster coalescence and Ostwald ripening, resulting in square-shaped crystalline Pt particles, independent of the initial cluster sizes. The respective sintering onset temperatures scale with the cluster footprint and thus size. Remarkably, while small encapsulated clusters can still diffuse as a whole, atom detachment and thus Ostwald ripening are successfully suppressed up to 823 K, i.e. 200 K above the H\"{u}ttig temperature that indicates the thermodynamic stability limit.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The metastability of supported metal nanoparticles limits their application in heterogeneous catalysis at elevated temperatures due to their tendency to sinter. One strategy to overcome these thermodynamic limits on reducible oxide supports is encapsulation via strong metal-support interaction (SMSI). While annealing-induced encapsulation is a well-explored phenomenon for extended nanoparticles, it is as yet unknown whether the same mechanisms hold for sub-nanometer clusters, where concomitant sintering and alloying might play a significant role. In this article, we explore the encapsulation and stability of size-selected Pt5, Pt10 and Pt19 clusters deposited on Fe3O4(001). In a multimodal approach using temperature-programmed desorption (TPD), x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), we demonstrate that SMSI indeed leads to the formation of a defective, FeO-like conglomerate encapsulating the clusters. By stepwise annealing up to 1023 K, we observe the succession of encapsulation, cluster coalescence and Ostwald ripening, resulting in square-shaped crystalline Pt particles, independent of the initial cluster sizes. The respective sintering onset temperatures scale with the cluster footprint and thus size. Remarkably, while small encapsulated clusters can still diffuse as a whole, atom detachment and thus Ostwald ripening are successfully suppressed up to 823 K, i.e. 200 K above the Hüttig temperature that indicates the thermodynamic stability limit.
6.
K D Briegel, F Riccius, J Filser, A Bourgund, R Spitzenpfeil, M Panighel, C Dri, B A J Lechner, F Esch
PyfastSPM: A Python package to convert 1D FastSPM data streams into publication quality movies Journal Article
In: SoftwareX, vol. 21, pp. 101269, 2022, ISSN: 2352-7110.
@article{nokey,
title = {PyfastSPM: A Python package to convert 1D FastSPM data streams into publication quality movies},
author = {K D Briegel and F Riccius and J Filser and A Bourgund and R Spitzenpfeil and M Panighel and C Dri and B A J Lechner and F Esch},
url = {https://www.sciencedirect.com/science/article/pii/S235271102200187X},
doi = {https://doi.org/10.1016/j.softx.2022.101269},
issn = {2352-7110},
year = {2022},
date = {2022-12-09},
urldate = {2022-12-09},
journal = {SoftwareX},
volume = {21},
pages = {101269},
abstract = {Since the invention of scanning probe microscopy, researchers have desired to use this technique to monitor sub-second surface dynamics with atomic spatial resolution. A recently presented add-on electronics module enables the speed-up of existing, conventional scanning probe microscopes without any modification of the actual instrument. The resulting one-dimensional (1D) data stream, recorded while the tip oscillates in a sinusoidal motion, has to be reconstructed into a layered rectangular matrix in order to visualize the movie. The Python-based pyfastspm package performs this conversion, while also correcting for sample tilt, noise frequencies, piezo creep, and thermal drift. Quick automatic conversion even of considerable batches of data is achieved by efficient algorithms that bundle time-expensive steps, such as interpolation based on Delaunay triangulation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Since the invention of scanning probe microscopy, researchers have desired to use this technique to monitor sub-second surface dynamics with atomic spatial resolution. A recently presented add-on electronics module enables the speed-up of existing, conventional scanning probe microscopes without any modification of the actual instrument. The resulting one-dimensional (1D) data stream, recorded while the tip oscillates in a sinusoidal motion, has to be reconstructed into a layered rectangular matrix in order to visualize the movie. The Python-based pyfastspm package performs this conversion, while also correcting for sample tilt, noise frequencies, piezo creep, and thermal drift. Quick automatic conversion even of considerable batches of data is achieved by efficient algorithms that bundle time-expensive steps, such as interpolation based on Delaunay triangulation.
5.
P Petzoldt, M Eder, S Mackewicz, M Blum, T Kratky, S Günther, M Tschurl, U Heiz, B A J Lechner
In: The Journal of Physical Chemistry C, vol. 126, no. 38, pp. 16127-16139, 2022, ISSN: 1932-7447.
@article{nokey,
title = {Tuning Strong Metal\textendashSupport Interaction Kinetics on Pt-Loaded TiO2(110) by Choosing the Pressure: A Combined Ultrahigh Vacuum/Near-Ambient Pressure XPS Study},
author = {P Petzoldt and M Eder and S Mackewicz and M Blum and T Kratky and S G\"{u}nther and M Tschurl and U Heiz and B A J Lechner},
url = {https://doi.org/10.1021/acs.jpcc.2c03851},
doi = {10.1021/acs.jpcc.2c03851},
issn = {1932-7447},
year = {2022},
date = {2022-09-29},
urldate = {2022-09-29},
journal = {The Journal of Physical Chemistry C},
volume = {126},
number = {38},
pages = {16127-16139},
abstract = {Pt catalyst particles on reducible oxide supports often change their activity significantly at elevated temperatures due to the strong metal\textendashsupport interaction (SMSI), which induces the formation of an encapsulation layer around the noble metal particles. However, the impact of oxidizing and reducing treatments at elevated pressures on this encapsulation layer remains controversial, partly due to the “pressure gap” between surface science studies and applied catalysis. In the present work, we employ synchrotron-based near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the effect of O2 and H2 on the SMSI-state of well-defined Pt/TiO2(110) catalysts at pressures of up to 0.1 Torr. By tuning the O2 pressure, we can either selectively oxidize the TiO2 support or both the support and the Pt particles. Catalyzed by metallic Pt, the encapsulating oxide overlayer grows rapidly in 1 × 10\textendash5 Torr O2, but orders of magnitude less effectively at higher O2 pressures, where Pt is in an oxidic state. While the oxidation/reduction of Pt particles is reversible, they remain embedded in the support once encapsulation has occurred.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Pt catalyst particles on reducible oxide supports often change their activity significantly at elevated temperatures due to the strong metal–support interaction (SMSI), which induces the formation of an encapsulation layer around the noble metal particles. However, the impact of oxidizing and reducing treatments at elevated pressures on this encapsulation layer remains controversial, partly due to the “pressure gap” between surface science studies and applied catalysis. In the present work, we employ synchrotron-based near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the effect of O2 and H2 on the SMSI-state of well-defined Pt/TiO2(110) catalysts at pressures of up to 0.1 Torr. By tuning the O2 pressure, we can either selectively oxidize the TiO2 support or both the support and the Pt particles. Catalyzed by metallic Pt, the encapsulating oxide overlayer grows rapidly in 1 × 10–5 Torr O2, but orders of magnitude less effectively at higher O2 pressures, where Pt is in an oxidic state. While the oxidation/reduction of Pt particles is reversible, they remain embedded in the support once encapsulation has occurred.
4.
P Petzoldt, M Eder, S Mackewicz, M Blum, T Kratky, S Günther, M Tschurl, U Heiz, B A J Lechner
In: The Journal of Physical Chemistry C, vol. 126, no. 38, pp. 16127-16139, 2022, ISSN: 1932-7447.
@article{nokey,
title = {Tuning Strong Metal\textendashSupport Interaction Kinetics on Pt-Loaded TiO2(110) by Choosing the Pressure: A Combined Ultrahigh Vacuum/Near-Ambient Pressure XPS Study},
author = {P Petzoldt and M Eder and S Mackewicz and M Blum and T Kratky and S G\"{u}nther and M Tschurl and U Heiz and B A J Lechner},
url = {https://doi.org/10.1021/acs.jpcc.2c03851},
doi = {10.1021/acs.jpcc.2c03851},
issn = {1932-7447},
year = {2022},
date = {2022-09-16},
urldate = {2022-09-16},
journal = {The Journal of Physical Chemistry C},
volume = {126},
number = {38},
pages = {16127-16139},
abstract = {Pt catalyst particles on reducible oxide supports often change their activity significantly at elevated temperatures due to the strong metal\textendashsupport interaction (SMSI), which induces the formation of an encapsulation layer around the noble metal particles. However, the impact of oxidizing and reducing treatments at elevated pressures on this encapsulation layer remains controversial, partly due to the “pressure gap” between surface science studies and applied catalysis. In the present work, we employ synchrotron-based near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the effect of O2 and H2 on the SMSI-state of well-defined Pt/TiO2(110) catalysts at pressures of up to 0.1 Torr. By tuning the O2 pressure, we can either selectively oxidize the TiO2 support or both the support and the Pt particles. Catalyzed by metallic Pt, the encapsulating oxide overlayer grows rapidly in 1 × 10\textendash5 Torr O2, but orders of magnitude less effectively at higher O2 pressures, where Pt is in an oxidic state. While the oxidation/reduction of Pt particles is reversible, they remain embedded in the support once encapsulation has occurred.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Pt catalyst particles on reducible oxide supports often change their activity significantly at elevated temperatures due to the strong metal–support interaction (SMSI), which induces the formation of an encapsulation layer around the noble metal particles. However, the impact of oxidizing and reducing treatments at elevated pressures on this encapsulation layer remains controversial, partly due to the “pressure gap” between surface science studies and applied catalysis. In the present work, we employ synchrotron-based near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the effect of O2 and H2 on the SMSI-state of well-defined Pt/TiO2(110) catalysts at pressures of up to 0.1 Torr. By tuning the O2 pressure, we can either selectively oxidize the TiO2 support or both the support and the Pt particles. Catalyzed by metallic Pt, the encapsulating oxide overlayer grows rapidly in 1 × 10–5 Torr O2, but orders of magnitude less effectively at higher O2 pressures, where Pt is in an oxidic state. While the oxidation/reduction of Pt particles is reversible, they remain embedded in the support once encapsulation has occurred.
3.
S Kaiser, F Maleki, K Zhang, W Harbich, U Heiz, S Tosoni, B A J Lechner, G Pacchioni, F Esch
Cluster Catalysis with Lattice Oxygen: Tracing Oxygen Transport from a Magnetite (001) Support onto Small Pt Clusters Journal Article
In: ACS Catalysis, vol. 11, no. 15, pp. 9519–9529, 2021.
@article{,
title = {Cluster Catalysis with Lattice Oxygen: Tracing Oxygen Transport from a Magnetite (001) Support onto Small Pt Clusters},
author = {S Kaiser and F Maleki and K Zhang and W Harbich and U Heiz and S Tosoni and B A J Lechner and G Pacchioni and F Esch},
url = {https://pubs.acs.org/doi/10.1021/acscatal.1c01451},
year = {2021},
date = {2021-07-16},
urldate = {2021-07-16},
journal = {ACS Catalysis},
volume = {11},
number = {15},
pages = {9519\textendash9529},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2.
A Böttcher, R Schwaiger, T M Pazdera, D Exner, J Hauns, D Strelnikov, S Lebedkin, R Gröger, F Esch, B A J Lechner
Nanoscale patterning at the Si/SiO2/graphene interface by focused He+ beam Journal Article
In: Nanotechnology, vol. 31, no. 50, pp. 505302, 2020, ISSN: 0957-4484.
@article{nokey,
title = {Nanoscale patterning at the Si/SiO2/graphene interface by focused He+ beam},
author = {A B\"{o}ttcher and R Schwaiger and T M Pazdera and D Exner and J Hauns and D Strelnikov and S Lebedkin and R Gr\"{o}ger and F Esch and B A J Lechner},
url = {https://iopscience.iop.org/article/10.1088/1361-6528/abb5cf/meta?casa_token=0ch84-BOwLoAAAAA:0ibNutoV58k0ONYDhRhhBtMaAbaDMOWEDghZKBvbCABbhx1dGH2gGSD1baUoc-Zosx5xyOGgxg},
doi = {10.1088/1361-6528/abb5cf},
issn = {0957-4484},
year = {2020},
date = {2020-10-06},
urldate = {2020-10-06},
journal = {Nanotechnology},
volume = {31},
number = {50},
pages = {505302},
abstract = {We have studied the capability of He+ focused ion beam (He+-FIB) patterning to fabricate defect arrays on the Si/SiO2/Graphene interface using a combination of atomic force microscopy (AFM) and Raman imaging to probe damage zones. In general, an amorphized 'blister' region of cylindrical symmetry results upon exposing the surface to the stationary focused He+ beam. The topography of the amorphized region depends strongly on the ion dose, DS, (ranging from 103 to 107ions/spot) with craters and holes observed at higher doses. Furthermore, the surface morphology depends on the distance between adjacent irradiated spots, LS. Increasing the dose leads to (enhanced) subsurface amorphization and a local height increase relative to the unexposed regions. At the highest areal ion dose, the average height of a patterned area also increases as ∼1/LS. Correspondingly, in optical micrographs, the µm2-sized patterned surface regions change appearance. These phenomena can be explained by implantation of the He+ ions into the subsurface layers, formation of helium nanobubbles, expansion and modification of the dielectric constant of the patterned material. The corresponding modifications of the terminating graphene monolayer have been monitored by micro Raman imaging. At low ion doses, DS, the graphene becomes modified by carbon atom defects which perturb the 2D lattice (as indicated by increasing D/G Raman mode ratio). Additional x-ray photoionization spectroscopy (XPS) measurements allow us to infer that for moderate ion doses, scattering of He+ ions by the subsurface results in the oxidation of the graphene network. For largest doses and smallest LS values, the He+ beam activates extensive Si/SiO2/C bond rearrangement and a multicomponent material possibly comprising SiC and silicon oxycarbides, SiOC, is observed. We also infer parameter ranges for He+-FIB patterning defect arrays of potential use for pinning transition metal nanoparticles in model studies of heterogeneous catalysis.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have studied the capability of He+ focused ion beam (He+-FIB) patterning to fabricate defect arrays on the Si/SiO2/Graphene interface using a combination of atomic force microscopy (AFM) and Raman imaging to probe damage zones. In general, an amorphized 'blister' region of cylindrical symmetry results upon exposing the surface to the stationary focused He+ beam. The topography of the amorphized region depends strongly on the ion dose, DS, (ranging from 103 to 107ions/spot) with craters and holes observed at higher doses. Furthermore, the surface morphology depends on the distance between adjacent irradiated spots, LS. Increasing the dose leads to (enhanced) subsurface amorphization and a local height increase relative to the unexposed regions. At the highest areal ion dose, the average height of a patterned area also increases as ∼1/LS. Correspondingly, in optical micrographs, the µm2-sized patterned surface regions change appearance. These phenomena can be explained by implantation of the He+ ions into the subsurface layers, formation of helium nanobubbles, expansion and modification of the dielectric constant of the patterned material. The corresponding modifications of the terminating graphene monolayer have been monitored by micro Raman imaging. At low ion doses, DS, the graphene becomes modified by carbon atom defects which perturb the 2D lattice (as indicated by increasing D/G Raman mode ratio). Additional x-ray photoionization spectroscopy (XPS) measurements allow us to infer that for moderate ion doses, scattering of He+ ions by the subsurface results in the oxidation of the graphene network. For largest doses and smallest LS values, the He+ beam activates extensive Si/SiO2/C bond rearrangement and a multicomponent material possibly comprising SiC and silicon oxycarbides, SiOC, is observed. We also infer parameter ranges for He+-FIB patterning defect arrays of potential use for pinning transition metal nanoparticles in model studies of heterogeneous catalysis.
1.
A Bourgund, B A J Lechner, M Meier, C Franchini, G S Parkinson, U Heiz, F Esch
Influence of Local Defects on the Dynamics of O-H Bond Breaking and Formation on a Magnetite Surface Journal Article
In: Journal of Physical Chemistry C, vol. 123, no. 32, pp. 19742-19747, 2019, ISSN: 1932-7447.
@article{,
title = {Influence of Local Defects on the Dynamics of O-H Bond Breaking and Formation on a Magnetite Surface},
author = {A Bourgund and B A J Lechner and M Meier and C Franchini and G S Parkinson and U Heiz and F Esch},
url = {\<Go to ISI\>://WOS:000481568900054},
doi = {10.1021/acs.jpcc.9b05547},
issn = {1932-7447},
year = {2019},
date = {2019-07-17},
urldate = {2019-07-17},
journal = {Journal of Physical Chemistry C},
volume = {123},
number = {32},
pages = {19742-19747},
keywords = {},
pubstate = {published},
tppubtype = {article}
}