Low‐Temperature Activation of Methane: It also Works Without a Transition Metal

Schröder, Detlef; Roithová, Jana

doi:10.1002/anie.200601273

Cited by 153 publications

(124 citation statements)

References 35 publications

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“…For the metal-oxide cations (right side of Table 1), the reaction of the cluster cation V 4 O 10 ϩ proceeds as a genuine H-atom abstraction (75) that is close to the KIE of Ϸ1.3 reported for H-atom abstraction by free OH radicals (80). H-atom abstraction from methane by MnO ϩ (51) and MgO ϩ (62) is also promoted by the radical character of the oxygen atom, although theory implies a significant participation of the metal and the formation of an insertion intermediate (62,81), as is reflected by the significant KIEs. MoO 3 ϩ exhibits a KIE of the same magnitude, thus pointing to the operation of a similar mechanism (60).…”

Section: Ligated Metal Cationssupporting

confidence: 69%

Gas-phase activation of methane by ligated transition-metal cations

Schröder

Schwarz²

2008

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

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237

135

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Motivated by the search for ways of a more efficient usage of the large, unexploited resources of methane, recent progress in the gas-phase activation of methane by ligated transition-metal ions is discussed. Mass spectrometric experiments demonstrate that the ligands can crucially influence both reactivity and selectivity of transition-metal cations in bond-activation processes, and the most reactive species derive from combinations of transition metals with the electronegative elements fluorine, oxygen, and chlorine. Furthermore, the collected knowledge about intramolecular kinetic isotope effects associated with the activation of C-H(D) bonds of methane can be used to distinguish the nature of the bond activation as a mere hydrogen-abstraction, a metal-assisted mechanism or more complex reactions such as formation of insertion intermediates or -bond metathesis.bond activation ͉ kinetic isotope effects ͉ mass spectrometry

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Section: Ligated Metal Cationssupporting

confidence: 69%

Gas-phase activation of methane by ligated transition-metal cations

Schröder

Schwarz²

2008

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

Self Cite

237

135

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“…Based on these previous findings, we propose that the C 3 H 6 O product resulting from an oxygen transfer from cationic, stoichiometric tungsten oxide clusters is probably propylene oxide, although we do not have experimental confirmation of this product assignment. Previous studies conducted by our group (54) and by others (56,57) . Spin-density calculations also reveal that the single unpaired electron is localized at the terminal oxygen atom with the elongated bond (57).…”

Section: Resultsmentioning

confidence: 65%

“…Spin-density calculations also reveal that the single unpaired electron is localized at the terminal oxygen atom with the elongated bond (57). Metal oxide clusters containing oxygen radicals have been found to be reactive for the selective oxidation of ethylene (54) and the activation of methane (56). Structural calculations on neutral (50) and anionic (46-48) tungsten oxide clusters illustrate that the stoichiometric species all contain terminal oxygen atoms that are bound exclusively in the atomic form.…”

Section: Resultsmentioning

confidence: 99%

Cluster reactivity experiments: Employing mass spectrometry to investigate the molecular level details of catalytic oxidation reactions

Johnson

Tyo

Castleman

2008

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

117

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Mass spectrometry is the most widely used tool in the study of the properties and reactivity of clusters in the gas phase. In this article, we demonstrate its use in investigating the molecular-level details of oxidation reactions occurring on the surfaces of heterogeneous catalysts via cluster reactivity experiments. Guided ion beam mass spectrometry (GIB-MS) employing a quadrupole-octopolequadrupole (Q-O-Q) configuration enables mass-selected cluster ions to be reacted with various chemicals, providing insight into the effect of size, stoichiometry, and ionic charge state on the reactivity of catalyst materials. For positively charged tungsten oxide clusters, it is shown that species having the same stoichiometry as the bulk, WO 3 ؉ , W2O 6 ؉ , and W3O 9 ؉ , exhibit enhanced activity and selectivity for the transfer of a single oxygen atom to propylene (C 3H6), suggesting the formation of propylene oxide (C 3H6O), an important monomer used, for example, in the industrial production of plastics. Furthermore, the same stoichiometric clusters are demonstrated to be active for the oxidation of CO to CO 2, a reaction of significance to environmental pollution abatement. The findings reported herein suggest that the enhanced oxidation reactivity of these stoichiometric clusters may be due to the presence of radical oxygen centers (W-O•) with elongated metal-oxygen bonds. The unique insights gained into bulk-phase oxidation catalysis through the application of mass spectrometry to cluster reactivity experiments are discussed.catalysis ͉ tungsten oxide ͉ oxygen radical ͉ carbon monoxide ͉ propylene M ass spectrometry has been crucial to the field of cluster research since its inception (1-9). A variety of cluster formation methods, primarily including laser vaporization (LaVa) (10-12), pulsed-arc discharge (PACIS) (13-15), electrospray ionization (ESI) (16), gas aggregation (17-18), and inert gas sputtering (CORDIS) (18) have enabled the creation of both positively and negatively charged as well as neutral gas-phase clusters across a large size range and with diverse elemental composition. The thermodynamic properties of clusters, including bond-dissociation energies (19-21), endothermic-reaction barriers (22), heat capacities (23), and the enthalpy, entropy, and free-energy changes associated with clustering reactions (24, 25), including those composed of hydrogen-bonded and van der Waals systems, have been widely studied, employing both GIB-MS and flow-tube experiments. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR) (26) along with other linear ion trapping techniques (27) have been used to investigate the time-dependent kinetics of cluster molecule reactions, providing insight into reaction mechanisms, activation energies, and reaction intermediates. The structural properties of clusters, including bonding motifs and collision cross-sections have been examined through collision-induced dissociation (CID) (28) and high-pressure drift cell experiments (29). Time-of-flight (TOF) mass spectrometry...

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“…A species as small as the diatomic magnesium oxide cation radical, MgO Á? , has been shown to activate the C-H bond of methane and to form methyl radicals [13]. It shares the O Á-radical site with the polynuclear (Al 2 O 3 ) 4 Á?…”

Section: Introductionmentioning

confidence: 99%

Models in Catalysis

2014

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The paper discusses the hierarchy of model studies with increasing complexity towards an understanding of industrial catalysts under reaction conditions. We use three case studies to document the progress in systems complexity as well as the development of instruments that allow us to approach the study of acting catalysts: magnesium oxide clusters in the gas phase, gold nanoparticles on metal oxide surfaces, and palladium nanoparticles compared to crystal surfaces. While the examples are from the field of heterogeneous catalysis, we discuss the relation to homogeneous and enzymatic catalysis.

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Low‐Temperature Activation of Methane: It also Works Without a Transition Metal

Cited by 153 publications

References 35 publications

Gas-phase activation of methane by ligated transition-metal cations

Gas-phase activation of methane by ligated transition-metal cations

Cluster reactivity experiments: Employing mass spectrometry to investigate the molecular level details of catalytic oxidation reactions

Models in Catalysis

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