Surface reactions of ethanol on UO2 thin film. Dehydrogenation and dehydration pathways

Abstract

The reaction of ethanol has been investigated on a UO2 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 (Tp) 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 1012 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 (CH3CHO) desorption, produced by the dehydrogenation of ethoxides, was sensitive to surface coverage. Tp changed from 640 K at θ = 0.06 to 610 K at θ = 1, while ethylene (CH2CH2) desorption, produced by the dehydration of ethoxides did not shift. The molar ratio of these two products (CH3CHO/CH2CH2) of 0.8 is similar to that previously found on a UO2(1 1 1) single crystal and fits with the UO bonding nature that contains a non-negligible fraction of covalency.