Abstract
The reaction of
CO
has been investigated on the surfaces of
UO
2
(
111
)
single crystal. Over the stoichiometric surface
CO
does not adsorb at
300
K
and no further reaction is noticed. Over
UO
2
−
x
(prepared by
Ar
+
bombardment),
CO
molecules adsorb and in presence of traces of
H
2
they couple to form acetylene molecules that desorb in two temperature domains during temperature programmed desorption (TPD). In the presence of excess
H
2
the coupling product is found to be ethylene. X-ray photoelectron spectroscopy (XPS) of the core level shows the presence of an
U
4
f
line at
377
eV
on the
UO
2
−
x
surface, attributed to
U
metal. This line disappears upon
CO
adsorption (
5
L
and above) at
300
K
; indicating oxidation of
U
metal atoms by
O
from dissociatively adsorbed
CO
. XPS
C
1
s
shows that the only
C
containing species formed is carbide. Computation of a
α
-
U
metal 2d-periodic slab was also conducted using plane-wave pseudopotential in the density functional theoretical framework. Two modes of
CO
adsorption were considered: molecular and dissociative. The dissociative adsorption was found more energetically favoured by
0.46
eV
. From TPD, XPS and computation results it is strongly suggested that
CO
is dissociatively adsorbed on
UO
2
−
x
and that a stable
U
–
C
species is formed at
300
K
.