Catalytic Non-Oxidative Coupling of Methane on Ta₈O₂⁺

Abstract

Mass-selected Ta8O2 + cluster ions catalyze the transformation of methane in a gas-phase ion trap experiment via nonoxidative coupling into ethane and H2, which is a prospective reaction for the generation of valuable chemicals on an industrial scale. Systematic variation of the reaction conditions and the isotopic labeling of methane by deuterium allow for an unambiguous identification of a catalytic cycle. Comparison with the proposed catalytic cycle for tantalum-doped silica catalysts reveals surprising similarities as the mechanism of the C–C coupling step, but also peculiar differences like the mechanism of the eventual formation of molecular hydrogen and ethane. Therefore, this work not only supplies insights into the mechanisms of methane coupling reactions but also illustrates how the study of trapped ionic catalysts can contribute to the understanding of reactions, which are otherwise difficult to study.

Recent advances in heterogeneous catalysis for the nonoxidative conversion of methane

“…Recently, free Ta 8 O 2 + cluster ions were also found to be capable of NOCM reactions. 58 A similar catalytic cycle for the C-C coupling step was proposed on the Ta 8 O 2 + cluster ions and the Ta-based catalyst (Fig. 8b), and the difference lies in the nal step of the product formation.…”

Carbid‐Dihydride: kohlenstoffhaltige Spezies identifiziert in der Ta4+‐vermittelten Methandehydrierung

“…Die Aktivität gegenüber Methan ist aber nicht nur auf Verbindungen mit einem einzelnen Tantalatom limitiert. Ta 8 O 2 + Cluster ermöglichen beispielsweise die nicht‐oxidative Kopplung von Methan in der Gasphase, [7] und nackte Ta 4 + Cluster weisen beachtliche Reaktionseigenschaften bezüglich der Methandehydrierung auf [8] . Bezüglich letztere betrifft dies vor allem die mögliche Struktur der Reaktionsprodukte und deren Reaktivität in Anbetracht der Bildung von Substanzen mit erhöhter Wertschöpfung in Folgereaktionen.…”

“…Die Aktivität gegenüber Methan ist aber nicht nur auf Verbindungen mit einem einzelnen Tantalatom limitiert. Ta 8 O 2 + Cluster ermçglichen beispielsweise die nicht-oxidative Kopplung von Methan in der Gasphase, [7] und nackte Ta 4…”

Carbide Dihydrides: Carbonaceous Species Identified in Ta4+‐Mediated Methane Dehydrogenation

“…[6] The activity towards methane is not only limited to single Ta atom compounds. Ta 8 O 2 + clusters, for example, enable the nonoxidative methane coupling in the gas phase, [7] and bare Ta 4 + clusters exhibit remarkable reaction properties in methane dehydrogenation. [8] For the latter, this concerns in particular the potential structure of the reaction products and their reactivity towards the formation of value-added product in subsequent reactions.…”

“…[4] Furthermore,c ationic tantalum oxides were identified to exhibit apeculiar reactivity (as for example apossible formation of CH 2 Oand CH 3 OH in the reaction with CH 4 ), [5] and at antalum atomic cation induces coupling of methane and carbon dioxide. [6] The activity towards methane is not only limited to single Ta atom compounds.T a 8 O 2 + clusters,f or example,e nable the nonoxidative methane coupling in the gas phase, [7] and bare Ta 4 + clusters exhibit remarkable reaction properties in methane dehydrogenation. [8] Fort he latter, this concerns in particular the potential structure of the reaction products and their reactivity towards the formation of value-added product in subsequent reactions.…”