Abstract
The reactions of acetone were investigated on
α
U
3
O
8
(stoichiometric and
H
2
reduced) by temperature programmed desorption. The surface and bulk characteristics of U oxides were investigated by x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD). The comparison between the XPS U 4
f
7/2
binding energy of
β
UO
3
,
α
U
3
O
8
,
and
UO
2
indicated that the U cations in
U
3
O
8
are composed of
+5/+6 (2/1)
or
+4/+6 (1/2)
oxidation states. XPS of
H
2
reduced
α
U
3
O
8
(at 800 K) indicated a shift of the
U
4f
7/2
binding energy from 381.6 (unreduced) to 380.5 eV (reduced) as well as the appearance of two satellites at 387.0 and 397.4 eV. These new XPS lines’ positions are characteristic of
U
+4
cations of
UO
2
.
Similar results were observed upon Ar-ion sputtering of
α
U
3
O
8
.
Ar-ion sputtering of
β
UO
3
also results in the reduction of
U
+6
cations to
U
+4
cations. XRD of
H
2
reduced
α
U
3
O
8
indicated that all of the
α
U
3
O
8
phase was transformed to the
UO
2
phase. A considerable difference between the reactivity of the surfaces of
U
3
O
8
and
UO
2
towards acetone was observed. A carbon–carbon bond formation reaction giving isobutene was observed only on the
α
U
3
O
8
surface indicating its structure-sensitive nature and/or its sensitivity towards changing the oxidation state of U cations. This reaction has not been observed on the surfaces of actinide oxides before. On the other hand, acetone reacted on
UO
2
to give mainly propene. This latter reaction (which is a C–O bond dissociation) is most likely due to the capacity of
UO
2
to accommodate large numbers of atomic oxygen in interstitial positions while maintaining its structure intact.