Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-ray Absorption Techniques

Bordiga, Silvia; Groppo, Elena; Agostini, Giovanni; Bokhoven, Jeroen A. van; Lamberti, Carlo

doi:10.1021/cr2000898

Cited by 592 publications

(646 citation statements)

References 1,612 publications

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“…Samples A, B and F were chosen because they showed sufficient X-ray absorption (that is, Ni weight loading), and because the particles on the catalysts were predominantly below 3 nm, which theoretically ensures > 35% surface atoms and thus sufficient signal in bulk Q-XAS to detect surface changes 42,43 . The larger particle sizes were chosen to verify observed trends.…”

Section: Nature Catalysismentioning

confidence: 99%

Unravelling structure sensitivity in CO2 hydrogenation over nickel

et al. 2018

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T he reduction of CO 2 emissions into the Earth's atmosphere is gaining legislative importance in view of its impact on the climate [1][2][3][4][5] . Reduction of the harmful effect of these emissions through reclamation of CO 2 is made attractive because CO 2 can be a zero-or even negative-cost carbon feedstock 6,7 . The conversion of renewably produced hydrogen and CO 2 into methane, or synthetic natural gas, over Ni is a solution that combines the potential to reduce CO 2 emissions with a direct answer to the temporal mismatch in renewable electricity production capacity and demand [8][9][10][11][12][13][14][15][16][17] . Chemical energy storage in the form of hydrogen production by electrolysis is a relatively mature technology; however, the required costly infrastructure, and inefficiencies in distribution and storage deem it inconvenient for large-scale application in the near future. Point-source CO 2 hydrogenation to methane represents an alternative approach with higher energy density. Furthermore, methane is more easily liquefied and can be stored safely in large quantities through infrastructures that already exist 18,19 . Power-to-gas (in this case methane) is thus actively considered as being capable of balancing electric grid stability, which will allow us to increase the renewable energy supply 20 .The search for fossil fuel alternatives, and application of a process such as that described above can arguably be achieved only with the help of advances in catalysis and the closely related field of nanomaterials. Continuous efforts in both fields have allowed us to make increasingly smaller and catalytically more active (metal) particles. However, it is already known that making progressively smaller supported catalyst particles does not necessarily linearly correspond to higher catalytic activity [21][22][23] . This phenomenon, where not all atoms in a supported metal catalyst have the same activity, is called structure sensitivity and is often attributed to the distinctly different chemistries on different lattice planes for π -bond activation in CO 2 , or σ -bond activation in, for example H 2 dissociation and C-H propagation 21,24 . The availability of stepped (less coordinated) versus terrace (more coordinated) sites on the surface of supported catalyst nanoparticles obviously changes with particle size, and atomic geometries become particularly interesting below 2 nm where, for example, π -bond activation is believed to not be able to occur 21 . While particle-size effects have been extensively studied for CO hydrogenation over Co 23,25 , the understanding of such structure sensitivity effects for these critical smaller metal particle sizes is lacking as sub-2-nm particles prove difficult to synthesize for first-row transition metals (Co, Fe and Ni). However, a particle-size effect for CO 2 hydrogenation is much less well established 26 .Here, we used a unique set of SiO 2 -supported Ni nanoparticles with diameters ranging from 1 to 7 nm in size, and show not only the existence of a distinct pa...

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Section: Nature Catalysismentioning

confidence: 99%

Unravelling structure sensitivity in CO2 hydrogenation over nickel

et al. 2018

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“…The investigation of these three portions of the XANES spectrum and the interpretation of the different physical phenomena governing their characteristic features provides plenty of information, both of electronic and structural nature [77,82,[89][90][91][92][93][94][95][96][97].…”

Section: X-ray Transient Absorption: Theoretical Background and Expermentioning

confidence: 99%

“…The features of the preedge peaks are directly influenced by the density of states and the occupancy of states; therefore, their investigation is extremely helpful in unravelling the electronic structure of molecules [77,82,98,99]. Moreover, the intensity of pre-edge peaks is governed by the selection rules for dipolar transitions, which can be relaxed depending on the local symmetry around the absorber atom [100].…”

Section: X-ray Transient Absorption: Theoretical Background and Expermentioning

confidence: 99%

“…The energy position of the absorption edge is sensitive to the oxidation state of the absorber [82,101,102] due to the charge-shielding effect on the ionization energy (practically, a higher oxidation number corresponds to an edge shift towards higher energies). In addition, the edge location is influenced by the coordination geometry, which ultimately is determined by the energy position of molecular orbitals [25].…”

Section: X-ray Transient Absorption: Theoretical Background and Expermentioning

confidence: 99%

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Synchrotron ultrafast techniques for photoactive transition metal complexes

Borfecchia

Garino

Salassa

et al. 2013

Phil. Trans. R. Soc. A.

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In the last decade, the use of time-resolved X-ray techniques has revealed the structure of lightgenerated transient species for a wide range of samples, from small organic molecules to proteins. Time resolutions of the order of 100 ps are typically reached, allowing one to monitor thermally equilibrated excited states and capture their structure as a function of time. This review aims at providing a general overview of the application of timeresolved X-ray solution scattering (TR-XSS) and time-resolved X-ray absorption spectroscopy (TR-XAS), the two techniques prevalently employed in the investigation of light-triggered structural changes of transition metal complexes. In particular, we herein describe the fundamental physical principles for static XSS and XAS and illustrate the theory of timeresolved XSS and XAS together with data acquisition and analysis strategies. Selected pioneering examples of photoactive transition metal complexes studied by TR-XSS and TR-XAS are discussed in depth.

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“…Recently, we undertook a thorough investigation of palladium-based catalysts supported on highly cross-linked porous polymers with and without functional groups [21][22][23]. In recent papers [21][22][23], we proved that the reduction of palladium precursor(palladium(II) acetate), in the presence of H2or CO, can be monitored by applying simultaneously Small-Angle X-ray Scattering (SAXS) [24][25][26] and X-ray Absorption Near Edge Structure (XANES) [27][28][29] techniques and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy [30][31][32] in operando conditions. We found that in presence of functional groups, such as the pyridyl group in poly(4-vinylpyridine-co-divinylbenzene), palladium (II) acetate is stabilized through the coordination of Pd 2+ cations, with the consequent rupture of the trimeric structure characteristic for solid palladium (II) acetate, and the restructuring of the acetate ligands in a monodentate coordination.…”

Section: Introductionmentioning

confidence: 99%

Formation and growth of palladium nanoparticles inside porous poly(4-vinyl-pyridine) monitored by operando techniques: The role of different reducing agents

et al. 2017

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In this work we followed the formation of palladium nanoparticles, starting from palladium (II) acetate precursor, inside a poly(4-vinylpyridine-co-divinylbenzene) polymer in presence of different reducing agents. The formation and growth of palladium nanoparticles in presence of H2was followed as a function of temperature by simultaneous XANES-SAXS techniques, coupled with DRIFT spectroscopy in operando conditions. It was found that the pyridyl functional groups in the polymer plays a fundamental role in the stabilization of the palladium (II) acetate precursor, as well as in the stabilization of the palladium nanoparticles. The effect of a thermal treatment in alcohol (ethanol and 2-propanol) was preliminarily investigated by means of DRIFT spectroscopy in operando conditions. We found that alcohols act as reducing agents for Pd(OAc)2. The obtained palladium nanoparticles were preliminarily characterized by means of IR spectroscopy using CO as probe molecule.

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Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-ray Absorption Techniques

Cited by 592 publications

References 1,612 publications

Unravelling structure sensitivity in CO2 hydrogenation over nickel

Unravelling structure sensitivity in CO2 hydrogenation over nickel

Synchrotron ultrafast techniques for photoactive transition metal complexes

Formation and growth of palladium nanoparticles inside porous poly(4-vinyl-pyridine) monitored by operando techniques: The role of different reducing agents

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