High-accuracy
quantum chemical calculations were carried out to
study the mechanisms and catalytic abilities of various mixed silicon
species Si
2
M with M = H, Li, Na, Cu, and Ag toward the
first step of methanol activation reaction. Standard heats of formation
of these small triatomic Si clusters were determined. Potential-energy
profiles were constructed using the coupled-cluster theory with extrapolation
to complete basis set CCSD(T)/CBS, and CCSD(T)/aug-cc-pVTZ-PP for
Si
2
Cu and Si
2
Ag. The most stable complexes generated
by the interaction of methanol with the mixed clusters Si
2
M possess low-spin states and mainly stem from an M–O connection
in preference to Si–O interaction, except for the Si
2
H case. In two competitive pathways including O–H and C–H
bond breakings, the cleavage of the O–H bond in the presence
of all clusters studied becomes predominant. Of the mixed clusters
Si
2
M considered, the dissociation pathways of both O–H
and C–H bonds with Si
2
Li turns out to have the lowest
energy barriers. The most remarkable finding is the absence of the
overall energy barrier for the O–H cleavage with the assistance
of Si
2
Li. The breaking of O–H and C–H bonds
with the assistance of Si
2
H, Si
2
Li, and Si
2
Na is kinetically preferred with respect to the Si
2
Cu and Si
2
Ag cases, apart from the case of Si
2
Na for O–H cleavage. In comparison with other transition-metal
clusters with the same size, such as Cu
3
, Pt
3
, and PtAu
2
, the energy barriers for the O–H bond
activation in the presence of small Si species, especially Si
2
H and Si
2
Li, are found to be lower. Consequently,
these small mixed silicon clusters can be regarded as promising alternatives
for the expensive metal-based catalysts currently used for methanol
activation particularly and other dehydrogenation processes of organic
compounds. The present study also suggests a further extensive search
for other doped silicon clusters as efficient and more realistic gas-phase
catalysts for important dehydrogenation processes in such a way that
they can be experimentally prepared and implemented.