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Comparative Study of Methanol Activation by Different Small Mixed Silicon Clusters Si2M with M = H, Li, Na, Cu, and Ag
journal contribution
posted on 2017-08-16, 08:15 authored by Tran Dieu Hang, Huynh Minh Hung, Minh Tho NguyenHigh-accuracy
quantum chemical calculations were carried out to
study the mechanisms and catalytic abilities of various mixed silicon
species Si2M 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
Si2Cu and Si2Ag. The most stable complexes generated
by the interaction of methanol with the mixed clusters Si2M possess low-spin states and mainly stem from an M–O connection
in preference to Si–O interaction, except for the Si2H 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
Si2M considered, the dissociation pathways of both O–H
and C–H bonds with Si2Li 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 Si2Li. The breaking of O–H and C–H bonds
with the assistance of Si2H, Si2Li, and Si2Na is kinetically preferred with respect to the Si2Cu and Si2Ag cases, apart from the case of Si2Na for O–H cleavage. In comparison with other transition-metal
clusters with the same size, such as Cu3, Pt3, and PtAu2, the energy barriers for the O–H bond
activation in the presence of small Si species, especially Si2H and Si2Li, 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.
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