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 CC
bond formation, shedding light on the plasma assistance of the essence.