Catalysis by ultrathin
LaBO₃ (B=Co, Fe) perovskite films

@article{Zeininger2021,

title = {Single-Particle Catalysis: Revealing Intraparticle Pacemakers in Catalytic H2 Oxidation on Rh},

author = {Johannes Zeininger and Yuri Suchorski and Maximilian Raab and Sebastian Buhr and Henrik Grönbeck and Günther Rupprechter},

doi = {10.1021/acscatal.1c02384},

year  = {2021},

date = {2021-07-27},

urldate = {2021-07-27},

journal = {ACS Catalysis},

volume = {11},

number = {15},

pages = {10020--10027},

publisher = {American Chemical Society (ACS)},

abstract = {Self-sustained oscillations in H_{2} oxidation on a Rh nanotip mimicking a single catalytic nanoparticle were studied by in situ field emission microscopy (FEM). The observed spatio-temporal oscillations result from the coupling of subsurface oxide formation/depletion with reaction front propagation. An original sophisticated method for tracking kinetic transition points allowed the identification of local pacemakers, initiating kinetic transitions and the nucleation of reaction fronts, with much higher temporal resolution than conventional processing of FEM video files provides. The pacemakers turned out to be specific surface atomic configurations at the border between strongly corrugated Rh{973} regions and adjacent relatively flat terraces. These structural ensembles are crucial for reactivity: while the corrugated region allows sufficient oxygen incorporation under the Rh surface, the flat terrace provides sufficient hydrogen supply required for the kinetic transition, highlighting the importance of interfacet communication. The experimental observations are complemented by mean-field microkinetic modeling. The insights into the initiation and propagation of kinetic transitions on a single catalytic nanoparticle demonstrate how in situ monitoring of an ongoing reaction on individual nanofacets can single out active configurations, especially when combined with atomically resolving the nanoparticle surface by field ion microscopy (FIM).},

keywords = {P08, TACO-associated},

pubstate = {published},

tppubtype = {article}

}

@article{Shen2021,

title = {Emerging applications of MXene materials in CO_{2} photocatalysis},

author = {Jiahui Shen and Zhiyi Wu and Chaoran Li and Chengcheng Zhang and Alexander Genest and Günther Rupprechter and Le He},

doi = {10.1016/j.flatc.2021.100252},

year  = {2021},

date = {2021-07-01},

journal = {FlatChem},

volume = {28},

pages = {100252},

publisher = {Elsevier BV},

abstract = {MXene materials, a young family of two-dimensional transition-metal carbides and nitrides, hold great promise for diverse demanding applications. Recently, it was discovered that MXenes can boost the efficiency of CO_{2} photocatalysis, e.g. by accelerating the charge separation, alleviating the photocorrosion, enhancing CO_{2} adsorption and activation, and promoting the photothermal conversion capability. In this mini-review, we summarize recent developments of photocatalysts based on MXene materials for various CO_{2} reduction reactions with a focus on the role of MXenes in photocatalytic processes. Several perspectives in terms of challenges and future research in this area are also highlighted.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Suchorski2021,

title = {Resolving multifrequential oscillations and nanoscale interfacet communication in single-particle catalysis},

author = {Yuri Suchorski and Johannes Zeininger and Sebastian Buhr and Maximilian Raab and Michael Stöger-Pollach and Johannes Bernardi and Henrik Grönbeck and Günther Rupprechter},

doi = {10.1126/science.abf8107},

year  = {2021},

date = {2021-06-18},

urldate = {2021-06-18},

journal = {Science},

volume = {372},

number = {6548},

pages = {1314--1318},

publisher = {American Association for the Advancement of Science (AAAS)},

abstract = {Metal nanoparticles used in heterogeneous catalysis can bear different facets with different reaction kinetics. Suchorski et al. used field electron microscopy with high spatial (∼2 nanometers) and time (∼2 milliseconds) resolution to study hydrogen oxidation on a curved rhodium crystal that displayed individual nanofacets. They also performed field ion microscopy of the water products. Periodic formation and depletion of subsurface oxygen blocked or allowed hydrogen adsorption, respectively, and led to oscillatory kinetics that could frequency lock between facets but at different frequencies. Surface reconstructions could also induce collapse of spatial coupling of oscillations.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Yang2021,

title = {Co_{3}O_{4}-CeO_{2} Nanocomposites for Low-Temperature CO Oxidation},

author = {Jingxia Yang and Nevzat Yigit and Jury Möller and Günther Rupprechter},

doi = {10.1002/chem.202100927},

year  = {2021},

date = {2021-04-29},

urldate = {2021-04-29},

journal = {Chemistry A European Journal},

publisher = {Wiley},

abstract = {In an effort to combine the favorable catalytic properties of Co_{3}O_{4} and CeO_{2}, nanocomposites with different phase distribution and Co_{3}O_{4} loading were prepared and employed for CO oxidation. Synthesizing Co_{3}O_{4}-modified CeO_{2} via three different sol-gel based routes, each with 10.4 wt % Co_{3}O_{4} loading, yielded three different nanocomposite morphologies:  CeO_{2}-supported Co_{3}O_{4} layers, intermixed oxides, and homogeneously dispersed Co. The reactivity of the resulting surface oxygen species towards CO were examined by temperature programmed reduction (CO-TPR) and flow reactor kinetic tests. The first morphology exhibited the best performance due to its active Co_{3}O_{4} surface layer, reducing the light-off temperature of  CeO_{2} by about 200 °C. In contrast, intermixed oxides and Co-doped  CeO_{2} suffered from lower dispersion and organic residues, respectively. The performance of Co_{3}O_{4}- CeO_{2} nanocomposites was optimized by varying the Co_{3}O_{4} loading, characterized by X-ray diffraction (XRD) and N_{2} sorption (BET). The 16–65 wt % _{3}O_{4}− CeO_{2} catalysts approached the conversion of 1 wt % Pt/CeO2, rendering them interesting candidates for low-temperature CO oxidation.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Rawool2021,

title = {Direct CO_{2} capture and conversion to fuels on magnesium nanoparticles under ambient conditions simply using water},

author = {Sushma A Rawool and Rajesh Belgamwar and Rajkumar Jana and Ayan Maity and Ankit Bhumla and Nevzat Yigit and Ayan Datta and Günther Rupprechter and Vivek Polshettiwar},

doi = {10.1039/d1sc01113h},

year  = {2021},

date = {2021-03-31},

urldate = {2021-03-31},

journal = {Chemical Science},

volume = {12},

number = {16},

pages = {5774--5786},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {Converting CO_{2} directly from the air to fuel under ambient conditions is a huge challenge. Thus, there is an urgent need for CO_{2} conversion protocols working at room temperature and atmospheric pressure, preferentially without any external energy input. Herein, we employ magnesium (nanoparticles and bulk), an inexpensive and the eighth-most abundant element, to convert CO_{2} to methane, methanol and formic acid, using water as the sole hydrogen source. The conversion of CO_{2} (pure, as well as directly from the air) took place within a few minutes at 300 K and 1 bar, and no external (thermal, photo, or electric) energy was required. Hydrogen was, however, the predominant product as the reaction of water with magnesium was favored over the reaction of CO_{2} and water with magnesium. A unique cooperative action of Mg, basic magnesium carbonate, CO_{2}, and water enabled this CO_{2} transformation. If any of the four components was missing, no CO_{2} conversion took place. The reaction intermediates and the reaction pathway were identified by ^{13}CO_{2} isotopic labeling, powder X-ray diffraction (PXRD), nuclear magnetic resonance (NMR) and in situ attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and rationalized by density-functional theory (DFT) calculations. During CO_{2} conversion, Mg was converted to magnesium hydroxide and carbonate, which may be regenerated. Our low-temperature experiments also indicate the future prospect of using this CO_{2}-to-fuel conversion process on the surface of Mars, where CO_{2}, water (ice), and magnesium are abundant. Thus, even though the overall process is non-catalytic, it could serve as a step towards a sustainable CO_{2} utilization strategy as well as potentially being a first step towards a magnesium-driven civilization on Mars.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Rupprechter2021,

title = {Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso-Scale Aggregates},

author = {Günther Rupprechter},

doi = {10.1002/smll.202004289},

year  = {2021},

date = {2021-03-10},

urldate = {2021-03-10},

journal = {Small},

publisher = {Wiley},

abstract = {Operando characterization of working catalysts, requiring per definitionem the simultaneous measurement of catalytic performance, is crucial to identify the relevant catalyst structure, composition and adsorbed species. Frequently applied operando techniques are discussed, including X-ray absorption spectroscopy, near ambient pressure X-ray photoelectron spectroscopy and infrared spectroscopy. In contrast to these area-averaging spectroscopies, operando surface microscopy by photoemission electron microscopy delivers spatially-resolved data, directly visualizing catalyst heterogeneity. For thorough interpretation, the experimental results should be complemented by density functional theory. The operando approach enables to identify changes of cluster/nanoparticle structure and composition during ongoing catalytic reactions and reveal how molecules interact with surfaces and interfaces. The case studies cover the length-scales from clusters via nanoparticles to meso-scale aggregates, and demonstrate the benefits of specific operando methods. Restructuring, ligand/atom mobility, and surface composition alterations during the reaction may have pronounced effects on activity and selectivity. The nanoscale metal/oxide interface steers catalytic performance via a long ranging effect. Combining operando spectroscopy with switching gas feeds or concentration-modulation provides further mechanistic insights. The obtained fundamental understanding is a prerequisite for improving catalytic performance and for rational design.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Winkler2021,

title = {How the anisotropy of surface oxide formation influences the transient activity of a surface reaction},

author = {Philipp Winkler and Johannes Zeininger and Yuri Suchorski and Michael Stöger-Pollach and Patrick Zeller and Matteo Amati and Luca Gregoratti and Günther Rupprechter},

doi = {10.1038/s41467-020-20377-9},

year  = {2021},

date = {2021-01-04},

urldate = {2021-01-04},

journal = {Nature Communications},

volume = {12},

number = {1},

publisher = {Springer Science and Business Media LLC},

abstract = {Scanning photoelectron microscopy (SPEM) and photoemission electron microscopy (PEEM) allow local surface analysis and visualising ongoing reactions on a µm-scale. These two spatio-temporal imaging methods are applied to polycrystalline Rh, representing a library of well-defined high-Miller-index surface structures. The combination of these techniques enables revealing the anisotropy of surface oxidation, as well as its effect on catalytic hydrogen oxidation. In the present work we observe, using locally-resolved SPEM, structure-sensitive surface oxide formation, which is summarised in an oxidation map and quantitatively explained by the novel step density (SDP) and step edge (SEP) parameters. In situ PEEM imaging of ongoing H_{2} oxidation allows a direct comparison of the local reactivity of metallic and oxidised Rh surfaces for the very same different stepped surface structures, demonstrating the effect of Rh surface oxides. Employing the velocity of propagating reaction fronts as indicator of surface reactivity, we observe a high transient activity of Rh surface oxide in H2 oxidation. The corresponding velocity map reveals the structure-dependence of such activity, representing a direct imaging of a structure-activity relation for plenty of well-defined surface structures within one sample.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Li2021,

title = {Sum frequency generation spectroscopy in heterogeneous model catalysis: a minireview of CO-related processes},

author = {Xia Li and Günther Rupprechter},

doi = {10.1039/d0cy01736a},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {Catalysis Science & Technology},

volume = {11},

number = {1},

pages = {12--26},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {Sum frequency generation (SFG) vibrational spectroscopy is a unique surface/interface-sensitive method, enabling the identification of chemical species and molecular structures, densities and orientations. SFG has been proven to be a powerful probe to examine adsorbates and reactions at solid–gas interfaces related to heterogeneous catalysis, employing well-defined ultra-high vacuum (UHV) grown model catalysts and UHV-compatible high-pressure reaction cells, enabling bridging both the materials and pressure gaps. SFG was thus among the first methods for ambient pressure surface science, enabling the characterization of “high pressure adsorbates”. In this mini-review, we provide an overview of SFG studies of CO-related processes in heterogeneous model catalysis. This includes pressure- and/or temperature-dependent CO adsorption on single crystals (platinum, palladium, rhodium, iridium, copper, nickel) and oxide/graphene-supported (palladium, platinum) nanoparticles, as well as CO reactions (oxidation/hydrogenation) simultaneously monitored by SFG and mass spectrometry. The adsorption of isotopic CO mixtures on single crystals and nanoparticles provides information on the individual contributions of vibrational coupling and chemical interactions to the adsorbate–adsorbate interactions. Altogether, SFG helps to identify various adsorption sites, adsorbate structures, molecular orientations and CO reactions on prototypical catalyst surfaces of increasing complexity. Specifically, the analysis of molecular orientation (tilt angles) can be carried out by polarization-dependent SFG.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Pramhaas2020,

title = {Interplay between CO Disproportionation and Oxidation: On the Origin of the CO Reaction Onset on Atomic Layer Deposition-Grown Pt/ZrO_{2} Model Catalysts},

author = {Verena Pramhaas and Matteo Roiaz and Noemi Bosio and Manuel Corva and Christoph Rameshan and Erik Vesselli and Henrik Grönbeck and Günther Rupprechter},

doi = {10.1021/acscatal.0c03974},

year  = {2020},

date = {2020-12-17},

urldate = {2020-12-17},

journal = {ACS Catalysis},

volume = {11},

number = {1},

pages = {208--214},

publisher = {American Chemical Society (ACS)},

abstract = {Pt/ZrO_{2} model catalysts were prepared by atomic layer deposition (ALD) and examined at mbar pressure by operando sum frequency generation (SFG) spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) combined with differentially pumped mass spectrometry (MS). ALD enables creating model systems ranging from Pt nanoparticles to bulk-like thin films. Polarization-dependent SFG of CO adsorption reveals both the adsorption configuration and the Pt particle morphology. By combining experimental data with ab initio density functional theory (DFT) calculations, we show that the CO reaction onset is determined by a delicate balance between CO disproportionation (Boudouard reaction) and oxidation. CO disproportionation occurs on low-coordinated Pt sites, but only at high CO coverages and when the remaining C atom is stabilized by a favorable coordination. Thus, under the current conditions, initial CO oxidation is found to be strongly influenced by the removal of carbon deposits formed through disproportionation mechanisms rather than being determined by the CO and oxygen inherent activity. Accordingly, at variance with the general expectation, rough Pt nanoparticles are seemingly less active than smoother Pt films. The applied approach enables bridging both the “materials and pressure gaps”.},

keywords = {P08, P10, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Haunold2020,

title = {An ultrahigh vacuum-compatible reaction cell for model catalysis under atmospheric pressure flow conditions},

author = {Thomas Haunold and Christoph Rameshan and Andrey V Bukhtiyarov and Günther Rupprechter},

doi = {10.1063/5.0026171},

year  = {2020},

date = {2020-12-01},

urldate = {2020-12-01},

journal = {Review of Scientific Instruments},

volume = {91},

number = {12},

pages = {125101},

publisher = {AIP Publishing},

abstract = {Atmospheric pressure reactions on model catalysts are typically performed in so-called high-pressure cells, with product analysis performed by gas chromatography (GC) or mass spectrometry (MS). However, in most cases, these cells have a large volume (liters) so that the reactions on catalysts with only cm^{2} surface area can be carried out only in the (recirculated) batch mode to accumulate sufficient product amounts. Herein, we describe a novel small-volume (milliliters) catalytic reactor that enables kinetic studies under atmospheric pressure flow conditions. The cell is located inside an ultrahigh vacuum chamber that is deliberately limited to basic functions. Model catalyst samples are mounted inside the reactor cell, which is locked to an oven for external heating and closed by using an extendable/retractable gas dosing tube. Reactant and product analyses are performed by both micro-GC and MS. The functionality of the new design is demonstrated by catalytic ethylene (C_{2}H_{4}) hydrogenation on polycrystalline Pt and Pd foils.},

keywords = {P08, P10, pre-TACO},

pubstate = {published},

tppubtype = {article}

}