Pt⁺-Catalyzed Oxidation of Methane:  Theory and Experiment

Abstract

The oxidation of methane with molecular oxygen using the atomic platinum cation as a catalyst, yielding methanol, formaldehyde, and higher oxidation products, has been studied both computationally and experimentally. The most relevant reaction pathways have been followed in detail. To this end a large number of stationary points, both minima and transition states, have been optimized using a hybrid density functional theory method (B3LYP). At these optimized geometries, energies have been calculated using both an empirical scaling scheme (PCI-80) and the B3LYP method employing extended basis sets with several polarization functions. Good agreement with available experimental data has been obtained. For the parts of the catalytic cycle where detailed experimental results have not been available, the new calculated results have complemented the experimental picture to reach an almost complete understanding of the reaction mechanisms. Spin−orbit effects have been incorporated using an empirical approach, which has lead to improved agreement with experiments. The new FTICR experiments reported in the present study have helped to clarify some of the most complicated reaction sequences.

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

“…With the increased knowledge gathered in recent years, both experimentally and theoretically, some mechanistic guidelines for the interpretation of the primary, intramolecular KIEs associated with the C-H(D) bond activation of methane can be provided, however. For the platinum species listed in the left side of Table 1, the KIEs are generally quite low, which is consistent with the view that for platinum not the activation step itself, but the release of the products is rate-determining (5,27,79). In contrast, a sizable KIE occurs in the case of the nickel(II) fluoride cation NiF ϩ , which is consistent with the view that this reaction proceeds as a -bond metathesis in which C-H(D) bond cleavage and H(D)-F bond formation contribute to the rate-determining step (40).…”

“…In the case of M ϭ Pt, also a catalytic variant with molecular oxygen leading to oxidized products such as methanol, formaldehyde, and formic acid could be realized (4,5), and for M ϭ Ta, a (stoichiometric) coupling of the initially formed TaCH 2 ϩ with CO 2 to afford ketene as a product was found (6,7). More recently, the details of these reactions, including those metals that cannot activate methane under thermal conditions, were analyzed by combined experimental and theoretical approaches, e.g., for M ϭ Fe (8), Ni (9), Zr (10), Hf (11), Mo (12), Ta (13), W (14), Re (15), Author contributions: D.S.…”

Chemie mit Methan: Studieren geht über Probieren!

“…[7] Um die Dehydrierung thermochemisch günstig zu gestalten, muss die Bindungsenergie D 0 (M-CH 2 ) der MetallMethyliden-Bindung grçßer sein als die Dehydrierungsenthalpie von Methan [Gleichung (5)].…”

“…Reaktion (9c) findet unter thermischen Bedingungen typischerweise nur mit Oxiden der 5d-Reihe statt. [7] In diesem Abschnitt konzentrieren wir uns auf die Eigenschaften jener Metalloxide, die für die Reaktion (9a) von besonderer Bedeutung sind, und in der das Insertionsintermediat H 3 C-M [64] oder in der Chemie von Metalloenzymen. [62] Am …”

Iron-Mediated Amination of Hydrocarbons in the Gas Phase

“…Although the neutral products cannot be detected directly, thermochemical data predict that the formation of nitrous acid in Reaction 8a is much more exergonic than that of NO OH, for example 13 ). However, a detailed theoretical analysis of a related system has demonstrated that the mechanistic course of metal-mediated O 2 activations can be rather complex [51]. As Fe is regenerated during the reaction, a catalytic protocol for the oxidation of NH 3 to HNO 2 involving the elementary Reactions 5, 2a, and 8a is conceivable 14 ).…”