Hydrogen Oxidation on Stepped Rh Surfaces: µm-Scale versus Nanoscale

Datler, Martin; Bespalov, Ivan; Buhr, S.; Zeininger, Johannes; Stöger-Pollach, Michael; Bernardi, Johannes; Rupprechter, Günther; Suchorski, Yuri

doi:10.1007/s10562-016-1824-4

Cited by 18 publications

(39 citation statements)

References 43 publications

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“…Similarly as for the Rh foil by PEEM, for catalytic studies on the Rh nanotip the FIM/FEM chamber was operated as a flow reactor, whereas FEM was used as a reaction imaging tool (resolution ~ 2 nm). The Rh nanotip (the same as was used in our recent study of H 2 oxidation [26]) was fabricated by electrochemical etching of a Rh wire (0.1 mm, Mateck, 99.99%) followed by field evaporation at 77 K in UHV for fine shaping and cleaning of the surface under Ne + FIM imaging control (with atomic resolution). The temperature of the tip was measured by a Ni/NiCr thermocouple spot-welded to its shank.…”

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%

“…To directly compare the µm-and nm-scale behaviour of CO oxidation on stepped Rh surfaces, the reaction was also studied by FEM using the same Rh nanotip that was used in our recent study of H 2 oxidation [26]. The FIM pictures with atomic resolution (Fig.…”

Section: Stepped Surfaces Of a Nm-sized Rh Tipmentioning

confidence: 99%

“…An ongoing catalytic reaction is visualized in real time by PEEM and the digital analysis of the in situ recorded PEEM video-files provides the required spatially-resolved kinetic information (kinetics by imaging [22]). A series of CO and H 2 oxidation studies on individual μm-sized low Miller index Pt and Pd domains, as well as on supported Pd particles, demonstrated the applicability and reliability of this approach [21][22][23][24][25][26].…”

Section: Introductionmentioning

confidence: 99%

“…Herein, we apply the same approach and the same polycrystalline Rh sample as in our recent study of H 2 oxidation on stepped Rh surfaces [26], but for CO oxidation, a reaction that has been extensively studied on platinum group metals due to its importance in automobile exhaust gases treatment. For rhodium, renewed interest is due to increasingly using Rh for the newest generation of automotive catalytic converters designed for direct injection gasoline engines working under lean-burn conditions (e.g.…”

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: Stepped Surfaces Of a Nm-sized Rh Tipmentioning

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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Catalysis by Imaging: From Meso- to Nano-scale

Suchorski

Rupprechter

2020

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In-situ imaging of catalytic reactions has provided insights into reaction front propagation, pattern formation and other spatio-temporal effects for decades. Most recently, analysis of the local image intensity opened a way towards evaluation of local reaction kinetics. Herein, our recent studies of catalytic CO oxidation on Pt(hkl) and Rh(hkl) via the kinetics by imaging approach, both on the meso- and nano-scale, are reviewed. Polycrystalline Pt and Rh foils and nanotips were used as µm- and nm-sized surface structure libraries as model systems for reactions in the 10–5–10–6 mbar pressure range. Isobaric light-off and isothermal kinetic transitions were visualized in-situ at µm-resolution by photoemission electron microscopy (PEEM), and at nm-resolution by field emission microscopy (FEM) and field ion microscopy (FIM). The local reaction kinetics of individual Pt(hkl) and Rh(hkl) domains and nanofacets of Pt and Rh nanotips were deduced from the local image intensity analysis. This revealed the structure-sensitivity of CO oxidation, both in the light-off and in the kinetic bistability: for different low-index Pt surfaces, differences of up to 60 K in the critical light-off temperatures and remarkable differences in the bistability ranges of differently oriented stepped Rh surfaces were observed. To prove the spatial coherence of light-off on nanotips, proper orthogonal decomposition (POD) as a spatial correlation analysis was applied to the FIM video-data. The influence of particular configurations of steps and kinks on kinetic transitions were analysed by using the average nearest neighbour number as a common descriptor. Perspectives of nanosized surface structure libraries for future model studies are discussed.

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Hydrogen Oxidation on Stepped Rh Surfaces: µm-Scale versus Nanoscale

Cited by 18 publications

References 43 publications

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

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

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

Catalysis by Imaging: From Meso- to Nano-scale

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