The adsorption and oxidation of acetic acid and acetaldehyde on Cu(110)

Abstract

Acetic acid adsorbed on Cu(110) at 140 K in a molecular state and XPS showed the double C 1s emission expected for this species. UPS emissions compatible with molecular acetic acid were observed, but the 13a' orbital exhibited a chemisorption bonding shift, indicating that the molecule binds to the surface through the oxygen non-bonding lone-pair orbital of the OH group. Upon heating to 370 K some acetic acid desorbed at 240 K, hydrogen was evolved at 310 K, and the O 1s spectrum narrowed revealing that the remaining tightly bound species possessed identical oxygen atoms. The coverage of the moiety was 3.5 × 10 14 cm -2. This species appears to be an acetate, and the outermost valence levels in the UPS closely resembled those observed for the formate. The acetate did not decompose until ∼590 K. The reaction products indicated the formation of another intermediate, acetic anhydride, which decomposed to yield mainly CO 2, CH 4, CH 3COOH, H 2C 2O (ketene), and carbon fragments. Oxygen preadsorption enhanced acetate formation and resulted in its presence in the photoelectron spectra even at 140 K; the oxygen removed the acid hydrogens to form water at low temperatures. Acetaldehyde adsorbed on the clean surface at 140 K in a molecular state and desorbed without reaction at 200 K. When oxygen was preadsorbed, acetaldehyde reacted with it to form the acetate.