Surface-Structure Libraries: Multifrequential Oscillations in Catalytic Hydrogen Oxidation on Rhodium

Suchorski, Yuri; Datler, Martin; Bespalov, Ivan; Zeininger, Johannes; Stöger-Pollach, Michael; Bernardi, Johannes; Grönbeck, Henrik; Rupprechter, Günther

doi:10.1021/acs.jpcc.8b11421

Cited by 19 publications

(44 citation statements)

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“…To study the processes on individual µm-sized domains of a polycrystalline foil, their exact crystallographic orientation must be determined first. For the present study, a Rh sample already previously characterized and used for H 2 oxidation [8,9] was employed ( Fig. 1c).…”

Section: Methodsmentioning

confidence: 99%

“…In this way spatially-resolved reaction kinetics for individual Rh(hkl) domains can be extracted by the local intensity analysis of PEEM images (kinetics by imaging [22], for applications see Refs. [8,9,21,[23][24][25][26]). Such measurements are Fig.…”

Section: Individual µM-sized Rh Domainsmentioning

confidence: 99%

“…Additionally, some stepped high-Miller-index fcc surfaces exhibit higher thermal and chemical stability both under reducing and oxidizing conditions [3,7]. Recently it was demonstrated that surface steps may not only be particularly 1 3 active sites, but they also influence the stability of the catalytically active state and can modulate kinetic oscillations [8,9]. Therefore, metal nanoparticles with high-Miller-index facets are beneficial for catalytic applications, but their synthesis is a challenging task, considering the energetics of crystal growth favouring low-index planes [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

“…In the present contribution, as an alternative approach we apply a surface structure library [9,20], i.e. a sample containing adjacent regions with different, but crystallographically well-defined orientations.…”

Section: Introductionmentioning

confidence: 99%

“…proper candidates. By determination of crystallographic orientation of the individual domains using electron backscatter diffraction (EBSD) such foils turn into real well-defined surface structure libraries [8,9,20,21]. Since the crystalline grains are in the 10-300 µm range, hundreds of individual domains with dozens of different orientations can be found on a 1 × 1 cm 2 foil.…”

Section: Introductionmentioning

confidence: 99%

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CO Oxidation on Stepped Rh Surfaces: μm-Scale Versus Nanoscale

et al. 2019

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The catalytic CO oxidation reaction on stepped Rh surfaces in the 10 −6 mbar pressure range was studied in situ on individual μm-sized high-Miller-index domains of a polycrystalline Rh foil and on nm-sized facets of a Rh tip, employing photoemission electron microscopy (PEEM) and field-ion/field-emission microscopy (FIM/FEM), respectively. Such approach permits a direct comparison of the reaction kinetics for crystallographically different regions under identical reaction conditions. The catalytic activity of the different Rh surfaces, particularly their tolerance towards poisoning by CO, was found to be strongly dependent on the density of steps and defects, as well as on the size (µm vs. nm) of the respective catalytically active surface. Graphic AbstractKeywords Surface reaction kinetics · PEEM · FEM/FIM · CO oxidation · Rhodium

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Section: Methodsmentioning

confidence: 99%

Section: Individual µM-sized Rh Domainsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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CO Oxidation on Stepped Rh Surfaces: μm-Scale Versus Nanoscale

et al. 2019

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Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

Rupprechter

2021

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described as metal dispersion (number of metal surface atoms relative to the total number of metal atoms in the catalyst), whereas the support is characterized by the specific surface area (m 2 g −1). For hemispherical metal particles of ≈1.5, 2, 5, and 10 nm diameter, the dispersion is about 0.8, 0.6, 0.3, and 0.1, respectively, illustrating why the nanoscale is required not to waste precious metal inside the particles. The ultimate dispersion is, of course, provided by single metal atoms and this concept is followed in "single atom catalysis" or "single site catalysis". [10-17] However, the adsorption and reaction steps of a catalytic reaction do typically not occur on isolated single atoms, but also involve neighboring sites, for example, of the oxide support [18] or of a metal matrix (for bimetallic nanoparticles, active metal atoms may be embedded in an inert or less-active metal matrix [11,19-23]). The so-called site isolation of active atoms may prevent CC bond cleavage (coking), which requires at least two neighboring active metals. In any case, the stability of the single atoms is the key challenge, as atoms may diffuse and sinter. Furthermore, for example, Pt, Pd, Cu, or Au atoms are mobilized by CO, [24-28] forming CO-M 1 units that may eventually sinter into larger clusters. Herein, we define metal clusters as entities with less than ≈100 atoms, characterizing the so-called "non-scalable" regime (Figure 1a). [29] Their atomic and electronic structure is significantly different from that of bulk metals, for example, with respect to atom positions (icosahedral vs face centered cubic fcc), distances (lattice contraction or expansion), and band structure (semiconductor vs metal). Clearly, these properties are size-dependent ("each atom counts" [30,31]), with pronounced impact on adsorption and reaction properties. [5,32] Accordingly, nanoparticles with more than ≈100 atoms are in the "scalableregime" and start to have or exhibit bulk atomic and electronic structure. [6,32-34] Nevertheless, the relative contributions of corner, edge, step, terrace and phase boundary sites on the surface of a nanoparticle (Figure 1b,c) are still size-dependent. [35,36] Meso-scale ("black") powders of metals are clearly bulk-like and have very low dispersion (Figure 1d), but the µm-sized aggregates still consist of adjoining nanocrystals with structured surfaces, comparable to that of true nanoparticles. 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 exper...

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