Can the state of platinum species be unambiguously determined by the stretching frequency of an adsorbed CO probe molecule?

Aleksandrov, Hristiyan A.; Neyman, Konstantin M.; Hadjiivanov, Konstantin; Vayssilov, Georgi N.

doi:10.1039/c6cp03988j

Cited by 136 publications

(146 citation statements)

References 61 publications

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“…The effect was demonstrated for Pt (111) and unsupported Pt particles as well as for ceria-supported Pt particles of different sizes 109,110 (Fig. 15).…”

Section: Identification Of the Oxidation State Of The Supported Catalmentioning

confidence: 88%

“…Density functional modeling reinforces the correlation between the stretching frequency and the particle size, on both unsupported and supported Pt particles. 109,110 In particular, the offset of the CO vibrational frequencies by 26 cm −1 with respect to Pt (111) indicates the formation of sub-nanometer-sized particles containing about 30 Pt atoms per particle. The findings both in UHV and under electrochemical conditions suggest that the conversion of atomically dispersed Pt 2+ to sub-nanometer sized Pt particles transforms the PtCeO x film into an electrocatalytically active state.…”

Section: Active State Of Pt-ceo 2 Thin Film Catalysts Under Electrochmentioning

confidence: 99%

“…20. The Pt-CeO 2 system was modeled as a low-energy vicinal surface exposing CeO 2 Ĳ111) terraces and step edges along the [110] direction accommodating Pt 2+ ions. These calculations showed that the barrier for H 2 dissociation at the Pt 2+ sites (1.2 eV) is even larger than the barrier for dissociation on the pristine CeO 2 Ĳ111) surface (1.0 eV).…”

Section: Supported Single Metal Atoms In the Absence Of Metal Particlesmentioning

confidence: 99%

“…However, general trends indicate that the vibrational frequency of the CO molecule in the ontop configuration depends on the distance between Pt and the nearest oxygen atom of ceria at which the platinum atom is bound to, and that CO vibrational frequencies increase as a function of the oxidation state of atomically dispersed Pt on ceria. 110 In addition, an increase in CO coverage leads to a widening of the CO frequency range for adsorption on supported Pt 8 clusters and to an increase of the frequency on Pt 2+ species.…”

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confidence: 99%

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Oxide-based nanomaterials for fuel cell catalysis: the interplay between supported single Pt atoms and particles

Lykhach

Bruix

Fabris

et al. 2017

Catal. Sci. Technol.

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The concept of single atom catalysis offers maximum noble metal efficiency for the development of lowcost catalytic materials. Among possible applications are catalytic materials for proton exchange membrane fuel cells. In the present review, recent efforts towards the fabrication of single atom catalysts on nanostructured ceria and their reactivity are discussed in the prospect of their employment as anode catalysts.The remarkable performance and the durability of the ceria-based anode catalysts with ultra-low Pt loading result from the interplay between two states associated with supported atomically dispersed Pt and subnanometer Pt particles. The occurrence of these two states is a consequence of strong interactions between Pt and nanostructured ceria that yield atomically dispersed species under oxidizing conditions and sub-nanometer Pt particles under reducing conditions. The square-planar arrangement of four O atoms on {100} nanoterraces has been identified as the key structural element on the surface of the nanostructured ceria where Pt is anchored in the form of Pt 2+ species. The conversion of Pt 2+ species to subnanometer Pt particles is triggered by a redox process involving Ce 3+ centers. The latter emerge due to either oxygen vacancies or adsorption of reducing agents. The unique properties of the sub-nanometer Pt particles arise from metal-support interactions involving charge transfer, structural flexibility, and spillover phenomena. The abundance of specific adsorption sites similar to those on {100} nanoterraces determines the ideal (maximum) Pt loading in Pt-CeO x films that still allows reversible switching between the atomically dispersed Pt and sub-nanometer particles yielding high activity and durability during fuel cell operation.

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“…The effect was demonstrated for Pt (111) and unsupported Pt particles as well as for ceria-supported Pt particles of different sizes 109,110 (Fig. 15).…”

Section: Identification Of the Oxidation State Of The Supported Catalmentioning

confidence: 88%

Section: Active State Of Pt-ceo 2 Thin Film Catalysts Under Electrochmentioning

confidence: 99%

Section: Supported Single Metal Atoms In the Absence Of Metal Particlesmentioning

confidence: 99%

mentioning

confidence: 99%

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Oxide-based nanomaterials for fuel cell catalysis: the interplay between supported single Pt atoms and particles

Lykhach

Bruix

Fabris

et al. 2017

Catal. Sci. Technol.

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“…In recent times, the CO-stretching frequency measured in IRAS has been used to differentiate between adatoms and nanoparticles 2 . The interpretation of such frequencies is somewhat controversial 6 , and an important role for surface science is to provide definitive vibrational frequencies to identify different species. The above described system, Au/MgO(100), is an excellent example of what can be achieved, and illustrates how complex the situation can be [7][8] .…”

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confidence: 99%

Unravelling single atom catalysis: The surface science approach

Parkinson

2017

Chinese Journal of Catalysis

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Understanding the fundamental mechanisms of single-atom catalysis (SAC) is important to design systems with improved performance and stability. This is problematic, however, because singleatom active sites are extremely difficult to characterize with existing experimental techniques. Over the last 40 years, surface science has provided the fundamental insights to understand heterogeneous catalysis, but model systems in which metal atoms are stable on well-characterized metal-oxide substrates at reaction temperatures are scarce. In this perspective, I discuss what is already known about isolated metal atoms adsorbed on model metal-oxide surfaces, and how this information can be used to understand SAC. A key issue is that, although the highly-idealised model systems studied in surface science may not be representative of a real working catalyst, they do very much resemble what can be calculated using state-of-the-art theoretical modelling. Thus, surface science offers an opportunity to rigorously benchmark the theoretical approach to modelling SAC in future. Perhaps more excitingly, several groups have developed model systems where metal adatoms remain stable at elevated temperatures. To date however, there has been no clear demonstration of catalytic activity. The perspective closes with a brief discussion of the prospect for STM experiments under realistic reaction conditions. Main TextThe rapidly emerging field of single-atom catalysis (SAC) aims to slash the precious metal loading in heterogeneous catalysts by replacing metal nanoparticles with so-called "single-atom" active sites 1 . While there are many reports of active SAC systems, the topic remains somewhat controversial because it is very difficult to characterize a system based on single atoms, and to distinguish between these and subnano particles 2 . In practice, most groups use aberration-corrected transmission electron microscopy (TEM) to demonstrate the atomic dispersion, sometimes supplemented by XANES, which can rule out significant metal-metal bonding 1 . The activity of the catalyst is then tested, and although some mechanistic information can be drawn by in-situ techniques such as IRAS, the catalytic mechanism is proposed largely on the basis of theoretical calculations. Such calculations are based on an idealised model of the system, in which both the support structure and active site geometry are assumed. Thus, a one-to-one correspondence between the experimental and theoretical results is difficult to prove.Traditionally, surface science has provided mechanistic information to understand heterogeneous catalysis. The idea is to strip away the complexity of a real catalyst and study well-defined singlecrystal samples in a highly-controlled ultrahigh vacuum (UHV) environment. This way, the adsorption of individual reactants can be studied in detail, and an understanding of the basic interactions can be built up. The downside of the approach is that the highly idealised model system may not be as representative of the real catalyst as o...

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Supported Metal Single‐Atom Thermocatalysts for Oxidation Reactions

Piccolo

Loridant

Christopher

2022

Supported Metal Single Atom Catalysis

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The interest in single-metal-atom dispersion in heterogeneous catalysis has existed since the 1950s with spectroscopic investigations of rhodium "single-site" catalysts supported on alumina, and more recently with oxometallate monomers for selective oxidation reactions. A decade ago, advances in electron microscopy intensified the interest of the catalysis community in controlling the dispersion of supported metals down to the single-atom active site level and revealing their intrinsic catalytic properties. Pioneering works in the ever-growing field of single-atom catalysis investigated late transition metals (group 8 to 11) supported on transition metal oxides for the CO oxidation and water-gas shift reactions. Since then, various single-atom catalysts, most often supported on oxides, have been evaluated in a broad panel of thermal oxidation reactions, and have often shown remarkable performances. Besides CO oxidation over oxidesupported noble metals, which represents the major part of the literature, this chapter reviews the main classes of oxidation reactions, including total and selective oxidations of hydrocarbons and oxygenates, on 2 oxide-or carbon-supported catalysts. Throughout the chapter, we emphasize several aspects that we consider important, such as the coordination environment and stability of single metal atoms, as well as their compared performance with supported nanoparticles. Figure 3. a) Aberration-corrected STEM image of Pt atoms (identified by yellow circles) on ca. 5 nm diameter anatase TiO2 particles. Adapted with permission from [72], Copyright 2017 ACS. b) CO probemolecule FTIR spectra of a Pt/TiO2 SAC as a function of temperature during a TPD measurement. c) DFT-calculated structure of CO bound to PtO2 adsorbed at a TiO2(145) step edge. b and c adapted with permission from [73], Copyright 2018 Elsevier. d) Schematic showing the structural transformation of isolated Pt species as a function of environmental conditions. Adapted with permission from [74],Copyright 2019 Springer Nature. e) DFT-calculated reaction pathway for CO oxidation on a Pd/TiO2 SAC that was supported by spectroscopic and kinetic analyses. Adapted with permission from [75],

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Can the state of platinum species be unambiguously determined by the stretching frequency of an adsorbed CO probe molecule?

Cited by 136 publications

References 61 publications

Oxide-based nanomaterials for fuel cell catalysis: the interplay between supported single Pt atoms and particles

Oxide-based nanomaterials for fuel cell catalysis: the interplay between supported single Pt atoms and particles

Unravelling single atom catalysis: The surface science approach

Supported Metal Single‐Atom Thermocatalysts for Oxidation Reactions

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