Comparative Study on the Reaction Pathways of 2‑Chloropropanoic Acid on Cu(100) and O/Cu(100)

CH3CHCOOH and CH3CHCOO have been theoretically predicted to be important in the decarboxylation or decarbonylation of propanoic acid on Pd(111). In the present study, we explore the possibility to prepare these two intermediates on Cu(100) and oxygen-predosed Cu(100) (O/Cu(100)), with CH3CHClCOOH as the precursor, and to investigate their adsorption geometries and reactions on the surfaces using X-ray photoelectron spectroscopy, reflection–absorption infrared spectroscopy, temperature-programmed reaction/desorption, and calculations of density functional theory. CH3CHClCOO and CH3CHCOO are suggested to be formed on Cu(100) at 250 K by heating the CH3CHClCOOH adsorption layers. However, CH3CHCOO can promptly recombine with the H from the deprotonation of CH3CHClCOOH to generate CH3CH2COO. The adsorbed propanoate decomposes mainly into H2, CO, and CO2 at a temperature higher than ∼380 K. On O/Cu(100), CH3CHClCOO is the predominant species found in the dissociation of CH3CHClCOOH at 250 K. The preadsorbed O disables the CH3CHCOO hydrogenation to form CH3CH2COO due to the lack of adsorbed H. This intermediate is not stable above ∼400 K and decomposes into H2, H2O, CO, and CO2, probably with a small amount of acrolein or methylketene. The CH3CHCOO is shown theoretically to be bonded on Cu(100) via the unsaturated carbon and one of the oxygen atoms.