Chemistry of fast electrons

Maximoff, Sergey N.; Head‐Gordon, Martin

doi:10.1073/pnas.0902030106

Cited by 43 publications

(40 citation statements)

References 42 publications

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“…As shown in Figure 10a, since the work function of metal Au (Φ m = 4.8 eV) is smaller than that of semiconductor TiO 2 (Φ s = 5.1 eV) [70], the electrons can diffuse from the metal into the semiconductor when the two phases are in contact [71,72]. This electron transfer was called "hot-electron flow" [56,57,[73][74][75] or "chemicurrent" [76][77][78], which usually happened in exothermic catalytic reactions [56,57,[73][74][75] and low-energy reactions [74] or even nonthermal directions [75]. For example, it has been reported that electron excitation was also involved in atomic/molecular adsorption processes [73,77,78].…”

Section: Proposed Electron Flow Processmentioning

confidence: 99%

Hydrogen-Etched TiO2−x as Efficient Support of Gold Catalysts for Water–Gas Shift Reaction

Song

Zhang

et al. 2018

Catalysts

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Hydrogen-etching technology was used to prepare TiO 2−x nanoribbons with abundant stable surface oxygen vacancies. Compared with traditional Au-TiO 2 , gold supported on hydrogen-etched TiO 2−x nanoribbons had been proven to be efficient and stable water-gas shift (WGS) catalysts. The disorder layer and abundant stable surface oxygen vacancies of hydrogen-etched TiO 2−x nanoribbons lead to higher microstrain and more metallic Au 0 species, respectively, which all facilitate the improvement of WGS catalytic activities. Furthermore, we successfully correlated the WGS thermocatalytic activities with their optoelectronic properties, and then tried to understand WGS pathways from the view of electron flow process. Hereinto, the narrowed forbidden band gap leads to the decreased Ohmic barrier, which enhances the transmission efficiency of "hot-electron flow". Meanwhile, the abundant surface oxygen vacancies are considered as electron traps, thus promoting the flow of "hot-electron" and reduction reaction of H 2 O. As a result, the WGS catalytic activity was enhanced. The concept involved hydrogen-etching technology leading to abundant surface oxygen vacancies can be attempted on other supported catalysts for WGS reaction or other thermocatalytic reactions.

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Section: Proposed Electron Flow Processmentioning

confidence: 99%

Hydrogen-Etched TiO2−x as Efficient Support of Gold Catalysts for Water–Gas Shift Reaction

Song

Zhang

et al. 2018

Catalysts

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“…The inverse of DEA to CO 2 , i.e. associative detachment, is thought to be important in the catalytic oxidation of CO on a metal surface [7]. In light of its fundamental importance to the understanding of such processes, it is noteworthy that the electronic structure of CO 2 and its metastable anions has not been completely characterized.…”

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confidence: 99%

Dissociative electron attachment to carbon dioxide via the 8.2 eV Feshbach resonance

Slaughter

Adaniya

Rescigno

et al. 2011

J. Phys. B: At. Mol. Opt. Phys.

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Momentum imaging experiments on dissociative electron attachment (DEA) to CO2 are combined with the results of ab initio calculations to provide a detailed and consistent picture of the dissociation dynamics through the 8.2 eV resonance, which is the major channel for DEA in CO2. The present study resolves several puzzling misconceptions about this system. PACS numbers: 34.80.HtNegative ion resonances are ubiquitous in low-energy electron-molecule collisions and provide an efficient vehicle for the transfer of electronic energy to nuclear motion either through vibrational excitation or dissociative electron attachment, the latter process resulting in the formation of both charged and neutral fragments. Recent dynamical studies [1] have shown that DEA to fundamental polyatomic systems can exhibit complex electronic and nuclear dynamics involving symmetry breaking target deformations [2] and, in some cases, conical intersections [3,4]. Mechanistic studies of the DEA process may give insight into their behavior in the condensed phase [5] and in biological environments [6].Carbon dioxide offers an interesting case in point. The inverse of DEA to CO 2 , i.e. associative detachment, is thought to be important in the catalytic oxidation of CO on a metal surface [7]. In light of its fundamental importance to the understanding of such processes, it is noteworthy that the electronic structure of CO 2 and its metastable anions has not been completely characterized. Most of the extant literature on low-energy electron-CO 2 scattering deals with the short-lived 2 Π u shape resonance near 4 eV, which provides the dominant mechanism for vibrational excitation, while experimental studies of DEA to CO 2 [8][9][10][11][12][13][14] have focused mainly on total cross sections and their dependence on electron energy and ion kinetic energy release. The 2 Π u resonance also feeds the CO( 1 Σ + ) + O − ( 2 P) DEA channel whose thermodynamic threshold lies at 3.99 eV. Scattering calculations [15] show that the 2 Π u resonance becomes sharper and finally electronically bound as the CO bonds are increased along the symmetric stretching coordinate. It is also known that the CO − 2 ion becomes stable upon bending. It was a long-held belief [16][17][18] [5,21], the 2 Π u resonance accounts for the other two states, then we are led to the puzzle whose resolution is a subject of this Letter. The dominant DEA channel in CO 2 is observed at 8.2 eV. Since this energy is less than the 10.0 eV required to produce electronically excited CO* + O − , the 8.2 eV resonance must necessarily result in electronic ground-state products. So how is this possible when, according to current thinking, all three states arising from this asymptote have already been accounted for? The early theoretical work of Claydon et al.[21] and England et al. [22] assigned the 8.2 eV peak to a 2 Σ + g shape resonance. This assignment has since been disputed. Srivastava and Orient [13], having found little or no dependence of the 8.2 eV DEA peak on vibrational excitation of the...

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“…99 Acid catalysis represents a unique chemistry that relies on charge transfer via protons and molecular ions, and many similarities appear to exist between SMSI and acid-base catalysis. The evolution of this work that began by measuring chemically induced charge flow at the oxide-metal interface [100][101][102] is quickly leading to a molecular level study of acid catalyzed chemistry with a focus on understanding the close relationship between charge flow and catalytic selectivity. Specifically, it is clear that a fundamental understanding of catalyst selectivity is closely related to understanding the flow of charge between various active sites on a catalyst.…”

Section: Methodsmentioning

confidence: 99%

Charge Transfer and Catalysis at the Metal Support Interface

Baker

2012

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Kinetic, electronic, and spectroscopic characterization of model Pt-support systems are used to demonstrate the relationship between charge transfer and catalytic activity and selectivity. The results show that charge flow controls the activity and selectivity of supported metal catalysts.Using a Pt/n-Si Schottky junction, it is possible to externally control the electronic properties at the Pt/Si interface by applying bias or by exciting charge carriers with visible light. It is found that this device can control the rate of CO oxidation on Pt. Results show that negative charge on the Pt increases the reaction rate while positive charge on the Pt decreases the reaction rate. This is the first time that a solid-state device has been used to externally control the rate of a chemical reaction as determined by directly measuring the product yield. Similar experiments were performed for the H 2 oxidation reaction and analogous results were obtained.Similarly, electronic control of catalyst performance can be achieved by substrate doping. It is shown that F doping can tune the electronic structure of TiO 2 . When F is incorporated into TiO 2 , the electrical conductivity is dramatically enhanced because F acts as an n-type dopant. It is shown that this highly n-type TiO 2 acts as an electronically active support for Pt catalysts, increasing the rate of CO oxidation by electronically activating surface O. It is further shown that for a multipath reaction, the electronic structure of TiO 2 also controls the reaction selectivity. The electronic activity of highly n-type TiO 2 serving as a Pt support for methanol oxidation selectively enhances the production of formaldehyde relative to CO 2 .Finally, sum frequency generation (SFG) vibrational spectroscopy is used to probe the molecular nature of strong metal-support interactions (SMSI). This is the first time that SFG has been used to probe the highly selective oxide-metal interface during catalytic reaction, and the results demonstrate that charge transfer from TiO 2 on a Pt/TiO 2 catalyst controls the product distribution of furfuraldehyde hydrogenation by an acid-base mechanism. SFG spectra reveal that a furfuryl-oxy intermediate forms on TiO 2 as a result of a charge transfer interaction. This furfuryl-oxy intermediate is a highly active and selective precursor to furfuryl alcohol, and spectral analysis shows that the Pt/TiO 2 interface is required primarily for H spillover. Density functional calculations predict that O-vacancies on the TiO 2 surface activate the formation of the furfuryl-oxy intermediate via an electron transfer to furfuraldehyde, drawing a strong analogy between SMSI and acid-base catalysis. 2This dissertation builds on extensive existing knowledge of metal-support interactions in heterogeneous catalysis. The results show the prominent role of charge transfer at catalytic interfaces to determine catalytic activity and selectivity. Further, this research demonstrates the possibility of selectively driving catalytic chemistry by controlling charge f...

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Chemistry of fast electrons

Cited by 43 publications

References 42 publications

Hydrogen-Etched TiO2−x as Efficient Support of Gold Catalysts for Water–Gas Shift Reaction

Hydrogen-Etched TiO2−x as Efficient Support of Gold Catalysts for Water–Gas Shift Reaction

Dissociative electron attachment to carbon dioxide via the 8.2 eV Feshbach resonance

Charge Transfer and Catalysis at the Metal Support Interface

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