XPS and NEXAFS study of the reactions of acetic acid and acetaldehyde over UO_2(100) thin film

摘要

The reactions of two C2 oxygenates, acetaldehyde (CH3CHO) and acetic acid (CH3COOH), over the (100) terminated surface of UO2thin film are investigated. The UO2film (ca. 100 nm thick) was prepared on a LaAlO3(100) substrate and its reactions were studied by high-resolution synchrotron X-ray photoelectron spectroscopy (XPS – C 1 s, O 1 s, and U 4f) and Near-Edge X-ray Absorption Fine Structure (NEXAFS – C K-edge). Results show a strong interaction of both molecules with the (100) surface at 300 K. Adsorption of acetic acid at 280 K produces acetates. Upon heating their population steadily decreased (XPS C 1 s) and some enolate or ketene-like species (such as CH2=COO(a)) are formed (NEXAFS). Acetaldehyde primarily adsorbed molecularly at 300 K and subsequent annealing to 480 K led to α-H abstraction making enolates upon interaction with surface O anions. No preferential orientation was detected for acetates while some could be seen for adsorbed acetaldehyde (NEXAFS). Results for the adsorption and reactivity of acetic acid and acetaldehyde on UO2(100) are compared with those of UO2(111) reported previously to further probe into possible structure-sensitive reactions of this actinide metal oxide.