Chemistry Reference
In-Depth Information
reactivities from those confined within nanotubes. The MONTs have more
complex electronic properties and crystal structures of metal oxides com-
pared to CNTs. Meanwhile, the MONTs maintain good chemical and
thermal stabilities with minimal power consumption and low weight
under different operating conditions. Most unique properties of MONTs
are mainly attributed to variety of oxidation states, coordination numbers,
symmetry, crystal-field stabilization, density, stoichiometry, and acid-base
surface properties.
11
As is known, one of the most interesting research fields of chemistry is
that of catalysis. Carbon materials and metal oxides have always been
playing significant roles in abundant reactions in chemical industries,
popularly as catalyst supports or catalysts themselves. It has demon-
strated that the enhanced catalysis performance is usually observed when
those materials transform from particles to tubular structures. A number
of experimental and theoretical studies on the effects of confinement in
CNTs and MONTs on catalysis have given solid evidence that the dif-
fusion, adsorption and reaction of molecules in the confined space are
quite different from that in the open space.
2,11,12,17
Understanding the
relationship between the tubular morphology of nanotubes and the
catalytic activity is absolutely an important issue from both fundamental
and industrial standpoints. However, the rational description of both the
properties of nanotubes and the structure-activity relationships suffers
from ambiguous interpretation due to a lack of atomistic investigations.
Thanks to the giant step forward provided by the development of com-
puter simulations
18
like quantum calculations (ab initio and density
functional theory (DFT)), grand canonical Monte-Carlo (GCMC) simu-
lations and molecular dynamics (MD) simulations, we can easily address
such as the geometrical and electronic structures of catalytic substrates,
the structural and energetic characterization and engineering of the ac-
tive sites present on the catalytic surface, the interactions between cata-
lyst supports and active phases, the nature of crucial intermediates and
the elementary steps of various catalytic reactions, all the knowledge of
which is mandatory for the design and optimization of tailor-made
catalysts for reactions with higher conversion and selectivity. Herein, we
report our simulated approaches to the exploration of structural, elec-
tronic and catalytic properties of CNTs and some prevailing MONTs
including TiO
2
, ZnO and V
2
O
5
NTs. The chemical modulations of
nanotubes are discussed briefly to improve the catalytic performances. In
particular, the adsorption ability of small gas molecules and the under-
going mechanisms of some chemical reactions on the three kinds of
pristine and modified MONTs with vacancy or doped variants are pre-
sented, together with others' investigstions.
2 Carbon nanotubes
In a computer simulation one is easy to build the structural models of
CNTs, which will be used as the substrates to investigate their confined,
surface modified and catalytic properties. The formation, geometric
structures and electronic properties of CNTs will not be involved in this
