Chemistry Reference
In-Depth Information
below Fermi level are well integrated with that of carbon, coupled
with similarity of PDOS between oxygen in CO and O
in
bonded with CO,
which can identify the formation of covalent bond between C and O
in
(Fig. 29e and f). However, the bond is not stronger than that of C-O, owing
to existence of weaker overlapped peaks between C and O
in
at -2 eV below
Fermi level. On the other hand, it is observed that three mixed PDOS
peaks exist at Fermi level for C, O
in
and V respectively, as shown in Fig. 29f
and h, which suggests that delocalized chemical bond may appear in the
three atoms and the valence electrons of CO may transfer to V atom via
O
in
atom. Generally, chemisorption of CO can effectively influence the
nature of V-O
in
bond and thereby pay a way for the formation of CO
3
. The
Hirshfeld charge population analysis indicates that for CO physisorption,
no charge transfer occurs between CO and V
2
O
5
nanotubes; whereas, after
CO chemisorption charge transfer occurs between the V and O
in
.
5.2.2 CO oxidation. CO oxidation was further investigated by the
lattice oxygen of V
2
O
5
(010) single layer and V
2
O
5
(5, 5) NTs, i.e. the de-
composition of carbonate, as shown in Fig. 30. It can be seen that the
reaction energy (-0.02 vs. -0.03 eV) and reaction barrier (0.40 vs. 0.43 eV)
on the single layer are nearly the same as that on the outside wall of NTs.
However, on the inside wall of NTs, the formation of CO
2
and an oxygen
vacancy from carbonate decomposition is exothermic by -0.17 eV, espe-
cially, the reaction barrier is 0.21 eV, which is half of that on the single
Fig. 30 Schematic energy diagrams for CO oxidation by lattice oxygen on the (a) surface,
(b) the outside and (c) inside wall of V
2
O
5
NTs. The reference system is COþV
2
O
5
NTs for
the inside and outside nanotube. The reference system is COþV
2
O
5
surface for the
calculation of surface. The optimized structures of transition state of CO
2
formation by CO
reaction with the lattice oxygen are (d) on the surface (e) on the outside, (f) inside wall of
V
2
O
5
NTs. The carbon atom, lattice oxygen, oxygen in carbon monoxide and vanadium
atom are represented by grey ball, red ball, pink ball and white ball, respectively. Bond
lengths are in Angstrom.
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