Gas-Phase Synthesis of Metal Olefins: Plasma-Assisted Methane Dehydrogenation and C═C Bond Formation

Abstract

Methane dehydrogenation and C–C coupling under mild conditions are very important but challenging in chemistry. Utilizing a customized time of flight mass spectrometer combined with a magnetron sputtering (MagS) cluster source, here, we have conducted a study on the reactions of methane with small silver and copper clusters simply by introducing methane in argon as the working gas for sputtering. Interestingly, a series of [M(C n H2n )]+ (M = Cu and Ag; n = 2–12) clusters were observed, indicating high-efficiency methane dehydrogenation in such a plasma-assisted chamber system. Density functional theory calculations find the lowest energy structures of the [M(C n H2n )]+ series pertaining to olefins indicative of both C–H bond activation of methane and C–C bond coupling. We analyzed the interactions involved in the [Cu­(C n H2n )]+ and [Ag­(C n H2n )]+ (n = 1–6) clusters and demonstrated the reaction coordinates for the “Cu+ + CH4” and “Ag+ + CH4.” It is illustrated that the presence of a second methane molecule enables us to reduce the necessary energy of dehydrogenation, which concurs with the experimental observation of an absence of the metal carbine products Cu+CH2 and Ag+CH2, which are short-lived. Also, it is elucidated that the higher-lying excitation states of Cu+ and Ag+ ions enable more favorable dehydrogenation process and CC bond formation, shedding light on the plasma assistance of the essence.

Graphene-Supported Single-Atom Ni as High-Performance Catalyst for Direct Methane-to-Methanol Conversion

“…The above conclusion is consistent with previous gas-phase studies of MO + catalyzing CH 4 to CH 3 OH that M = Ni affords the best reactivity and selectivity among M = Ni, Pd, and Pt. − This inspiring agreement indicates that gas-phase studies on simple molecules/ions are powerful to predict the catalytic behavior of heterogeneous catalysts that bear the same functional units. − …”

Experimental Reactivity of (MoO3)NO– (N = 1–21) Cluster Anions with C1–C4 Alkanes: A Simple Model to Predict the Reactivity with Methane

“…However, because of the high C–H bond strength, high molecular symmetry, and very stable electronic structures, the activation and conversion of methane usually occur under harsh conditions. , To activate and convert methane under ambient conditions, which is considered as the “holy grail” in chemistry, , a profound understanding of the mechanism of CH 4 activation is of utmost importance. Investigations on the reactions of CH 4 with gas-phase metal clusters under well-controlled conditions can provide detailed insights into the elementary steps at a molecular level (refs − are a selected but not comprehensive list of articles from different research groups on this topic). Metal oxide surfaces can generate a variety of reactive oxygen species, playing a crucial role in the activation of alkane molecules. − Studying the reactions of metal oxide clusters with methane under gas-phase conditions is important for understanding methane activation by reactive oxygen species.…”