A Stable Single‐Site Palladium Catalyst for Hydrogenations

Vilé, Gianvito; Albani, Davide; Nachtegaal, Maarten; Chen, Zupeng; Dontsova, Dariya; Antonietti, Markus; López, Núria; Pérez‐Ramírez, Javier

doi:10.1002/anie.201505073

Cited by 842 publications

(584 citation statements)

References 36 publications

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“…The photon excitation leads to electron transfer from the apical oxygen O3 to the center Ti atom, reducing the Ti 4+ to the Ti 3+ cation. Then the resulting Ti 3+ ions react with the ambient CO 2 and H 2 O, leading to their reduction and the formation of final products such as CH 4 and CH 3 OH (40). The products noted in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…ultrafast electron microscopy | single-site photocatalysis | titanium based photocatalyst | ulatrafast phenomena | time-resolved microscopy S ingle-site catalysts of both the thermally and photoactivated kind now occupy a prominent place in industrial-and laboratory-scale heterogeneous catalysis (1)(2)(3)(4)(5)(6)(7)(8). Among the most versatile of these are the ones consisting of coordinatively unsaturated transition metal ions (Ti, Cr, Fe, Mn.…”

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On the dynamical nature of the active center in a single-site photocatalyst visualized by 4D ultrafast electron microscopy

Yoo

Thomas

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Understanding the dynamical nature of the catalytic active site embedded in complex systems at the atomic level is critical to developing efficient photocatalytic materials. Here, we report, using 4D ultrafast electron microscopy, the spatiotemporal behaviors of titanium and oxygen in a titanosilicate catalytic material. The observed changes in Bragg diffraction intensity with time at the specific lattice planes, and with a tilted geometry, provide the relaxation pathway: the Ti 4+ =O 2− double bond transformation to a Ti 3+ −O 1− single bond via the individual atomic displacements of the titanium and the apical oxygen. The dilation of the double bond is up to 0.8 Å and occurs on the femtosecond time scale. These findings suggest the direct catalytic involvement of the Ti 3+ −O 1− local structure, the significance of nonthermal processes at the reactive site, and the efficient photo-induced electron transfer that plays a pivotal role in many photocatalytic reactions.ultrafast electron microscopy | single-site photocatalysis | titanium based photocatalyst | ulatrafast phenomena | time-resolved microscopy S ingle-site catalysts of both the thermally and photoactivated kind now occupy a prominent place in industrial-and laboratory-scale heterogeneous catalysis (1-8). Among the most versatile of these are the ones consisting of coordinatively unsaturated transition metal ions (Ti, Cr, Fe, Mn. . .) that occupy substitutional sites in well-defined, three-dimensionally extended, open-structure silicates of the zeolite type. The well-known and most widely used are the 4-or 5-coordinated Ti(IV) ions accommodated within the crystalline phase of silica, silicalite (9-14).Titanosilicates, especially, are used extensively both industrially and in the laboratory for a wide range of chemo-, regio-, and shapeselective oxidations of organic compounds (15-18). These single-site heterogeneous photocatalysts are quite distinct from those typified by TiO 2 , SrTiO 3 , and other titaniferous photocatalysts where the Ti(IV) ions are in 6-coordination; and where, in interpreting the processes involved in harnessing solar radiation, electronic band structure considerations hold sway in preference to the localized states (see, e.g., refs. 19, 20). It has been demonstrated (16-18, 21, 22) that single-site, coordinatively unsaturated Ti(IV)-centered photocatalysts are especially useful in the aerial oxidation of environmental pollutants in the photodegradation of NO (to N 2 and O 2 ), of H 2 O (to H 2 and O 2 ), and in the photocatalytic reduction of CO 2 to yield methanol. There is an exigent need to explore the precise nature of the electronic, temporal, and spatial changes accompanying the initial act of photoabsorption that sets in train the ensuing elementary chemical processes that are of vital environmental significance in, for example, the utilization of anthropogenic CO 2 as a chemical feedstock (23).Here, we report the use of 4D ultrafast electron microscopy (UEM) (24-26) to trace the spatiotemporal behavior of the Ti(IV) and O ...

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

On the dynamical nature of the active center in a single-site photocatalyst visualized by 4D ultrafast electron microscopy

Yoo

Thomas

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…43 There are enough examples in the literature that the irreversible adsorption of CO is weakened and even can become undetectable, if the metal species are in an ionic/electrondeficient state. 14,15,19,43 Moreover, Vile et al 19 did not detect any adsorption of CO on single ionic Pd atoms supported on carbon nitride, while these atoms were very active in some hydrogenation reactions.…”

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confidence: 99%

Single Atoms of Pt-Group Metals Stabilized by N-Doped Carbon Nanofibers for Efficient Hydrogen Production from Formic Acid

et al. 2016

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Formic acid is a valuable chemical derived from biomass, as it has a high hydrogen-storage capacity and appears to be an attractive source of hydrogen for various applications. Hydrogen production via formic acid decomposition is often based on using supported catalysts with Pt-group metal nanoparticles. In the present paper, we show that the decomposition of the acid proceeds more rapidly on single metal atoms (by up to one order of magnitude). These atoms can be obtained by rather simple means through anchoring Pt-group metals onto mesoporous N-functionalized carbon nanofibers. A thorough evaluation of the structure of the active site by aberration-corrected scanning transmission electron microscopy (ac-STEM) in high-angle annular dark field (HAADF) mode, by CO chemisorption, X-ray photoelectron spectroscopy (XPS) and quantum-chemical calculations reveals that the metal atom is coordinated by a pair of pyridinic nitrogen atoms at the edge of graphene sheets. The chelate binding provides an ionic/electron-deficient state of these atoms prevents their aggregation and thereby leads to an excellent stability under the reaction conditions. Catalysts with single atoms have also shown very high selectivity. Evidently, the findings can be extended to hydrogen production from other chemicals and can be helpful for improving other energy-related and environmentally benign catalytic processes.

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“…Recently, several studies [27][28][29][30][31][32][33][34][35][36][37] have provided incontrovertible proof that individual atoms are indeed capable of effecting a number of catalytic reactions, especially selective hydrogenations, as well as the water-gas shift reaction:…”

Section: Single-atom Heterogeneous Catalystsmentioning

confidence: 99%

“…Clearly, the nature of the bonding between the SAC and its support is crucial. An ingenious way of boosting the stability and minimizing the tendency for surface diffusion was devised by Perez-Ramirez and co-workers [34] and further discussed by Thomas [35] My group at Cambridge with Midgley, Leary, Furnvial et al [45,46] have recently been collaborating with Perez-Ramirez et al to investigate such systems as Ir on C 3 N 4 -the support described by Vilé et al [34]-which, in its graphitic form, has monatomic depressions into which SACs like Pd fit snugly ( figure 10). This catalyst is active in the three-phase selective partial hydrogenation of alkynes in flow mode, and both in activity and selectivity surpasses those of nanoparticle Pd.…”

Section: Single-atom Heterogeneous Catalystsmentioning

confidence: 99%

Reflections on the value of electron microscopy in the study of heterogeneous catalysts

Thomas

2017

Proc. R. Soc. A.

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Electron microscopy (EM) is arguably the single most powerful method of characterizing heterogeneous catalysts. Irrespective of whether they are bulk and multiphasic, or monophasic and monocrystalline, or nanocluster and even single-atom and on a support, their structures in atomic detail can be visualized in two or three dimensions, thanks to high-resolution instruments, with sub-Ångstrom spatial resolutions. Their topography, tomography, phase-purity, composition, as well as the bonding, and valence-states of their constituent atoms and ions and, in favourable circumstances, the short-range and long-range atomic order and dynamics of the catalytically active sites, can all be retrieved by the panoply of variants of modern EM. The latter embrace electron crystallography, rotation and precession electron diffraction, X-ray emission and high-resolution electron energy-loss spectra (EELS). Aberration-corrected (AC) transmission (TEM) and scanning transmission electron microscopy (STEM) have led to a revolution in structure determination. Environmental EM is already playing an increasing role in catalyst characterization, and new advances, involving special cells for the study of solid catalysts in contact with liquid reactants, have recently been deployed.

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A Stable Single‐Site Palladium Catalyst for Hydrogenations

Cited by 842 publications

References 36 publications

On the dynamical nature of the active center in a single-site photocatalyst visualized by 4D ultrafast electron microscopy

On the dynamical nature of the active center in a single-site photocatalyst visualized by 4D ultrafast electron microscopy

Single Atoms of Pt-Group Metals Stabilized by N-Doped Carbon Nanofibers for Efficient Hydrogen Production from Formic Acid

Reflections on the value of electron microscopy in the study of heterogeneous catalysts

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