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

Li, Xia; Rupprechter, Günther

doi:10.1039/d0cy01736a

Cited by 19 publications

(34 citation statements)

References 117 publications

(215 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The interfacial molecular orientations can be determined in an SFG experiment because the measured χ eff (2) is related to the macroscopic second-order susceptibility in the laboratory coordinates (χ ijk (2) ) by where e (ω i ) refers to the unit electric field vector and L (ω i ) is the Fresnel factor determined by the laser incidence and refraction angles, polarizations, and refractive indices. ,,, Furthermore, χ ijk (2) is related to the microscopic hyperpolarizability tensor elements β i ′ j ′ k ′ (2) in the molecular coordinate system through Euler transformation ⟨ R ii ′ R jj ′ R kk ′ ⟩ by Here, N s is the effective molecular surface number density per unit. For CO with C ∞v symmetry, the molecules have a random azimuthal distribution, and the surface CO orientation (tilt angle θ, the CO molecular axis with respect to the surface normal) can be determined by measuring I PPP / I SSP for a known molecular hyperpolarizability ratio R (i.e., R = β aac (2) /β ccc (2) = β bbc (2) /β ccc (2) ), assuming a δ-function for the orientation distribution. , …”

Section: Methodsmentioning

confidence: 99%

“…The SFG cell can be operated from 2.5 × 10 –8 mbar to 1 bar pressure and at 100–800 K. SFG measurements were performed using a 20 ps mode-locked Nd:YAG laser system (EKSPLA, PL2241) with a fundamental radiation of 1064 nm (30 mJ/pulse, 50 Hz repetition rate). A tunable mid-infrared beam (with the photon energy ω IR ) and a visible beam with a fixed wavelength of 532 nm were directed in a co-propagation geometry toward the Ir(111) surface (for details, see refs , , ), with incidence angles of 55° and 58.5° with respect to the surface normal, respectively. The pulse energy was 90–130 μJ for infrared between 1850 and 2150 cm –1 and 30 ± 5 μJ for visible.…”

Section: Methodsmentioning

confidence: 99%

“…For CO with C ∞v symmetry, the molecules have a random azimuthal distribution, and the surface CO orientation (tilt angle θ, the CO molecular axis with respect to the surface normal) can be determined by measuring I PPP /I SSP for a known molecular hyperpolarizability ratio R (i.e., R = β aac (2) /β ccc (2) = β bbc (2) / β ccc (2) ), assuming a δ-function for the orientation distribution. 25,42 2.2. UHV Preparation/Analysis Chamber Coupled to a UHV-High-Pressure Cell for SFG Spectroscopy.…”

Section: Basic Theory Of Polarization-dependent Sfgmentioning

confidence: 99%

See 2 more Smart Citations

CO Adsorption and Disproportionation on Smooth and Defect-Rich Ir(111)

Haunold

Werkovits

et al. 2022

J. Phys. Chem. C

Self Cite

View full text Add to dashboard Cite

CO adsorption and dissociation on “perfect” and “defect-rich” Ir(111) surfaces were studied by a combination of surface-analytical techniques, including polarization-dependent (PPP and SSP) sum frequency generation (SFG) vibrational spectroscopy, low-energy electron diffraction (LEED), Auger electron spectroscopy, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. CO was found to be ordered and tilted from the surface normal at high coverage on the “perfect” surface (e.g., θ = 30° at 0.70 ML), whereas it was less ordered and preferentially upright (θ = 4–10°) on the “defect-rich” surface for coverages of 0.55–0.70 ML. SFG, LEED, and XPS revealed that CO adsorption at low pressure/high temperature and high pressure/low temperature was reversible. In contrast, upon heating to ∼600 K in near mbar CO pressure, “perfect” and even more “defect-rich” Ir(111) surfaces were irreversibly modified by carbon deposits, which, according to DFT, result from CO disproportionation.

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Basic Theory Of Polarization-dependent Sfgmentioning

confidence: 99%

See 1 more Smart Citation

CO Adsorption and Disproportionation on Smooth and Defect-Rich Ir(111)

Haunold

Werkovits

et al. 2022

J. Phys. Chem. C

Self Cite

View full text Add to dashboard Cite

show abstract

“…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

“…The study of ions at interfaces has revealed a wealth of vital information on many fundamental chemical systems and processes, for example, surface catalysis, − atmospheric aerosol chemistry, , and electrochemistry. , Many of these studies have focused on the air–water interface, wherein detailed advances have been made in elucidating the mechanism of ion adsorption , and a molecular level picture of the solvation environment at the interface. − Equally important for developing a more detailed understanding of how small, inorganic ions behave at interfaces, the liquid–liquid interface warrants further examination. Specifically, the oil–water interface can serve as a model system to untangle water–hydrophobe interactions in complex environments, such as proteins in solution and biological membranes. , …”

mentioning

confidence: 99%

Characterizing Anion Adsorption to Aqueous Interfaces: Toluene–Water versus Air–Water

Devlin

McCaffrey

Saykally

2021

J. Phys. Chem. Lett.

View full text Add to dashboard Cite

We continue our investigation of the behavior of simple ions at aqueous interfaces, employing the combination of two surface-sensitive nonlinear spectroscopy tools, broadband deep UV electronic sum-frequency generation and UV second harmonic generation, to characterize the adsorption of thiocyanate to the interface of water with toluenea prototypical hydrophobe. We find that both the interfacial spectrum and the Gibbs free energy of adsorption closely match results previously reported for the air–water interface. We observe no relative spectral shift in the higher-energy CTTS transition of thiocyanate, implying similar solvation environments for the two interfaces. Similarly, the Gibbs free energies of adsorption agree within error; however, we expect the respective enthalpic and entropic contributions to differ between the two interfaces, similar to our earlier findings for the air–water versus graphene–water interfaces. Further experiments and theoretical modeling are necessary to quantify the mechanistic differences.

show abstract

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

Abstract: Sum frequency generation (SFG) vibrational spectroscopy is applied to ambient pressure surface science studies of adsorption and catalytic reactions at solid/gas interfaces.

Cited by 19 publications

References 117 publications

CO Adsorption and Disproportionation on Smooth and Defect-Rich Ir(111)

CO Adsorption and Disproportionation on Smooth and Defect-Rich Ir(111)

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

Characterizing Anion Adsorption to Aqueous Interfaces: Toluene–Water versus Air–Water

Contact Info

Product

Resources

About