Chemistry Reference
In-Depth Information
Fig. 9 The potential energy diagram of O
2
(a)
,
H
2
(b) dissociation on different sites of
Pd
10
/CNTs and Au
5
Pd
5
/CNTs, and the PDOS of Pd on different sites of Pd
10
/CNTs and
Au
5
Pd
5
/CNTs (c). The Fermi level is represented at 0 eV.
22
d-band center model. The adsorption and activation of H
2
follows the
similar rules with that of O
2
(Fig. 9b). Specially, two dimensional Pd rod
model for O
2
adsorption was employed and was found to perform the same
property as the metallic Pd cluster. In other words, the adsorption of H
2
on
Pd ensemble in the bottom layer is much weaker than that on the top layer.
The activation of H
2
is very facile on Pd sites of Pd
10
/CNTs with only
0.03 eV. While the activation energy on the Pd sites of bottom layer of
Au
5
Pd
5
/CNTs is 0.34 eV. It is seen that the activation and mobile of
hydrogen on Au
5
Pd
5
/CNTs are very facile, thus the atomic hydrogen in
these elementary reactions was considered in order to simplify these pro-
cesses. Therefore, the carbon support and the Au indeed have an inhibiting
effect on O
2
dissociation by reducing the oxygen adsorption capacity.
2.3.2 H
2
O
2
synthesis. The main elementary reactions of H
2
O
2
for-
mation by the hydrogenation of molecular oxygen are as follows:
O
2
þ
*
-
O
2
*
(1)
O
2
*
þ
H*
-
OOH*
(2)
