Surface reactions of ethanol on UO$_2$ thin film. Dehydrogenation and dehydration pathways

The reaction of ethanol has been investigated on a UO$_2$ thin film by temperature programmed desorption. Two
channels for ethanol desorption are identified. The first, in the 250–500 K region, is coverage dependent while
the second with a maximum peak temperature (T$_P$) at ca. 630 K is not. The desorption energy, Ed, of the second
channel is found to be equal to ca. 150 kJ/mol with a prefactor of 10$^{12}$ s$^{-1}$ and a desorption order n - 2.
This is attributed to surface ethoxides re-combinative desorption. This second desorption channel is accompanied by the
desorption of acetaldehyde (and hydrogen) and ethylene (and water). Acetaldehyde (CH$_3$CHO) desorption,
produced by the dehydrogenation of ethoxides, was sensitive to surface coverage. Its T$_P$ changed from 640 K at θ
= 0.06 to 610 K at θ = 1, while ethylene (CH$_2$––CH$_2$) desorption Tp, produced by the dehydration of ethoxides
did not shift. The molar ratio of these two products (CH$_3$CHO/CH$_2$––CH$_2$) of 0.8 is similar to that previously
found on a UO$_2$ (1 1 1) single crystal and fits with the U–O bonding nature that contains a non-negligible fraction
... mehrof covalency.