Chemistry Reference
In-Depth Information
OOH*
þ
H*
-
H
2
O
2
*
(3)
H
2
O
2
*
-
H
2
O
2
(g)
þ
*
(4)
It is seen that molecular oxygen (O
2
), hydroperoxo (OOH) and hydro-
gen peroxide (H
2
O
2
) are three key species for H
2
O
2
synthesis. Once these
key species decompose (eqs (5-7)), the H
2
O is easily formed.
O
2
*
-
2O*
(5)
OOH*
-
O*
þ
OH*
(6)
H
2
O
2
*
-
OH*
þ
OH*
(7)
We investigated the elementary reactions of the formation of H
2
O
2
and
decomposition of three key intermediates on AuPd and Pd ensemble of
the most stable Au
5
Pd
5
/CNTs (Fig. 10). After the adsorption of molecular
oxygen, two successive hydrogenation steps are necessary. The reaction
barriers of the OOH and H
2
O
2
formation on Pd ensemble of Au
5
Pd
5
/CNTs
are 0.75 and 0.69 eV, respectively, while on AuPd they are 0.26 and
Fig. 10 Potential energy diagram for the elementary reaction (H
2
O
2
formation (black
solid line), O
2
dissociation (red solid line), OOH dissociation (green solid line) H
2
O
2
de-
composition (pink solid line)) on AuPd (a), Pd ensembles (b) of Au
5
Pd
5
/CNTs and the
optimized transition states structures (side view) of the elementary steps on two active
sites (c). The bond lengths are given in angstrom.
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