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change of the formal oxidation state of the underlying 2f-cus Ru atoms from
þ
IV 2/3 to
þ
III 2/3. This change in the oxidation state upon chlorination
(being closer to
þ
IV) suggests that Cl exerts a stabilizing influence on the
RuO
2
(110) surface.
The surface reaction of HCl oxidation over chlorinated RuO
2
(110) is
summarized in Figure 8.4 in the form of a catalytic cycle. Both O
2
and HCl
adsorb dissociatively on the partly chlorinated RuO
2
(110) surface, where part
of the bridging O atoms are replaced by bridging Cl atoms (Cl
br
).
7
The ad-
sorption energy of oxygen is 200 kJ mol
1
with respect to O
2
molecules in the
gas phase forming O
ot
species.
94
The adsorption energy of the first HCl is
125 kJ mol
1
, where hydrogen from HCl is directly transferred to the
d
n
9
r
4
n
g
|
8
.
Figure 8.4
In the HCl oxidation reaction (the Deacon process) over RuO
2
(110) both
reactants, O
2
and HCl, adsorb dissociatively. Subsequently, surface
oxygen is reduced to the by-product water by H stemming from dissocia-
tive HCl adsorption. Water desorbs around 420 K, and the remaining
adsorbed chlorine atoms can recombine to form the desired product Cl
2
at temperatures around 600 K. Besides surface reactions, the Deacon
process is governed by the adsorption/desorption equilibria of Cl
2
,O
2
,
H
2
O, and HCl gases with the catalyst's surface, leading to reaction
inhibitions for the cases of H
2
O, Cl
2
and to promotion for the case of
O
2
and HCl. All energies given are calculated by DFT calculations.
8,103
DE
defines the adsorption energies which determine the dynamic adsorp-
tion/desorption equilibrium between the surface and the gas phase.
Copyright
r
2012 American Chemical Society.
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