A modeling analysis of molecular orientation at interfaces by polarization-dependent sum frequency generation vibrational spectroscopy

Li, Xia; Rupprechter, Günther

doi:10.1016/s1872-2067(19)63357-7

Cited by 9 publications

(10 citation statements)

References 97 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For other in situ/operando vibrational spectroscopy of active catalyst materials we refer to the literature (e.g., Raman [77][78][79][80][81]85,[122][123][124][125]163] and SFG [159,160,[169][170][171][172] ). The same ATR setup can also be used to study solid/liquid interfaces.…”

Section: Infrared Spectroscopy (Ftir Drifts Atr)mentioning

confidence: 99%

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

Rupprechter

2021

Small

Self Cite

View full text Add to dashboard Cite

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...

show abstract

Section: Infrared Spectroscopy (Ftir Drifts Atr)mentioning

confidence: 99%

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

Rupprechter

2021

Small

Self Cite

View full text Add to dashboard Cite

show abstract

“…When combined with a suitable UHV-to-high pressure cell, 6 − 12 SFG is a powerful in situ tool to obtain valuable information about adsorption sites, molecular orientation, polarizability, and changes thereof. 12 − 15 …”

Section: Introductionmentioning

confidence: 99%

“…L ii (ω i ) denotes the Fresnel factor at frequency ω i for the local field corrections, which can be calculated with the knowledge of incidence angles (α i ), refraction angles, and refractive indices. 3,5,15,37,38 χ ijk…”

Section: Introductionmentioning

confidence: 99%

“…Obviously, catalytic processes operate at higher temperatures and at pressures at and above 1 atm, leading to the so-called “pressure-gap” problem. , In contrast to the aforementioned techniques, sum frequency generation (SFG) vibrational spectroscopy, − a photon-in and photon-out technique, is inherently surface-sensitive even at atmospheric gas pressure. When combined with a suitable UHV-to-high pressure cell, − SFG is a powerful in situ tool to obtain valuable information about adsorption sites, molecular orientation, polarizability, and changes thereof. − …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Coverage-Induced Orientation Change: CO on Ir(111) Monitored by Polarization-Dependent Sum Frequency Generation Spectroscopy and Density Functional Theory

Pramhaas

Rameshan

et al. 2020

J. Phys. Chem. C

Self Cite

View full text Add to dashboard Cite

Polarization-dependent sum frequency generation (SFG) spectroscopy was applied to study the adsorption of carbon monoxide (CO) on the well-ordered (annealed) Ir(111) single-crystal surface at various CO coverages. Coverage was adjusted by varying the substrate temperature (300–575 K) and/or gas pressure (10 –7 to 1.0 mbar). Under all conditions investigated, only a single absorption band at 2038–2094 cm –1 was observed, characteristic of linearly bonded (on-top) CO. Using different polarizations, PPP and SSP spectra were acquired with a high signal-to-noise ratio, whereby tilt angles of CO on Ir(111) could be determined for the first time by SFG. It was found that not only the vibrational frequency of on-top CO but also the tilt angle was strongly coverage-dependent. The higher the coverage was, the larger the vibrational frequency and the tilt angle were. At about 0.7 ML coverage, a CO tilt angle of at least 20° was observed, which is in good agreement with density functional theory (DFT) calculations. In addition, the molecular hyperpolarizability ratio ( R ) of CO (at 0.13 ML in UHV) was determined to be 0.08. Based on the combined SFG/DFT results, it may change to 0.29 at 0.77 ML coverage.

show abstract

“…PPP/SSP), or the ratio of CH 3-sym /CH 3-asym of the PPP spectrum, the orientation angle of adsorbates can be quantitatively determined. 32,33,46 In addition, SFG spectroscopy has also been widely applied for solid-liquid interfaces [9][10][11][12]70,71 and liquid-liquid interfaces, [72][73][74][75][76][77][78] related to electrochemistry, polymers, surfactants, biomolecules and others, and has been extended to SFG microscopy. 46,79,80…”

Section: Catalysis Science and Technology Mini Reviewmentioning

confidence: 99%

Sum frequency generation spectroscopy in heterogeneous model catalysis: a minireview of CO-related processes

Rupprechter

2021

Catal. Sci. Technol.

Self Cite

View full text Add to dashboard Cite

show abstract

A modeling analysis of molecular orientation at interfaces by polarization-dependent sum frequency generation vibrational spectroscopy

Cited by 9 publications

References 97 publications

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

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

Coverage-Induced Orientation Change: CO on Ir(111) Monitored by Polarization-Dependent Sum Frequency Generation Spectroscopy and Density Functional Theory

Sum frequency generation spectroscopy in heterogeneous model catalysis: a minireview of CO-related processes

Contact Info

Product

Resources

About